User sync fails user picture

If updating a user picture there it gives first:

Warning: Invalid argument supplied for foreach() in mailjet_sync_single_user() (line 476 of / /web/modules/contrib/mailjet/mailjet.module) #0 / /web/core/includes/bootstrap.inc(584): _drupal_error_handler_real(2, 'Invalid argumen...', '/srv/www/habina...', 476, Array) #1 / /web/modules/contrib/mailjet/mailjet.module(476): _drupal_error_handler(2, 'Invalid argumen...', '/srv/www/habina...', 476, Array) #2 / /web/modules/contrib/mailjet/mailjet.module(427): mailjet_sync_single_user(Object(Drupal\user\Entity\User), 'update') #3 [internal function]: mailjet_user_update(Object(Drupal\user\Entity\User)) #4 / /web/core/lib/Drupal/Core/Extension/ModuleHandler.php(403): call_user_func_array('mailjet_user_up...', Array) #5 / /web/core/lib/Drupal/Core/Entity/EntityStorageBase.php(204): Drupal\Core\Extension\ModuleHandler->invokeAll('user_update', Array) #6 / /web/core/lib/Drupal/Core/Entity/ContentEntityStorageBase.php(773): Drupal\Core\Entity\EntityStorageBase->invokeHook('update', Object(Drupal\user\Entity\User)) #7 / /web/core/lib/Drupal/Core/Entity/EntityStorageBase.php(507): Drupal\Core\Entity\ContentEntityStorageBase->invokeHook('update', Object(Drupal\user\Entity\User)) #8 / /web/core/lib/Drupal/Core/Entity/ContentEntityStorageBase.php(658): Drupal\Core\Entity\EntityStorageBase->doPostSave(Object(Drupal\user\Entity\User), true) #9 / /web/core/lib/Drupal/Core/Entity/EntityStorageBase.php(432): Drupal\Core\Entity\ContentEntityStorageBase->doPostSave(Object(Drupal\user\Entity\User), true) #10 / /web/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php(774): Drupal\Core\Entity\EntityStorageBase->save(Object(Drupal\user\Entity\User)) #11 / /web/core/lib/Drupal/Core/Entity/Entity.php(390): Drupal\Core\Entity\Sql\SqlContentEntityStorage->save(Object(Drupal\user\Entity\User)) #12 / /web/modules/contrib/jsonapi/src/Controller/FileUpload.php(136): Drupal\Core\Entity\Entity->save() #13 [internal function]: Drupal\jsonapi\Controller\FileUpload->handleFileUploadForExistingResource(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\jsonapi_extras\ResourceType\ConfigurableResourceType), 'user_picture', Object(Drupal\user\Entity\User)) #14 / /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #15 / /web/core/lib/Drupal/Core/Render/Renderer.php(582): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #16 / /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #17 / /web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #18 / /vendor/symfony/http-kernel/HttpKernel.php(151): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #19 / /vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #20 / /web/modules/contrib/simple_oauth/src/HttpMiddleware/BasicAuthSwap.php(67): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 / /web/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Drupal\simple_oauth\HttpMiddleware\BasicAuthSwap->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 / /web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 / /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 / /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 / /web/modules/contrib/jsonapi/src/StackMiddleware/FormatSetter.php(41): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #26 / /web/modules/contrib/cdn/src/StackMiddleware/DuplicateContentPreventionMiddleware.php(119): Drupal\jsonapi\StackMiddleware\FormatSetter->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #27 / /web/core/modules/ban/src/BanMiddleware.php(50): Drupal\cdn\StackMiddleware\DuplicateContentPreventionMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #28 / /web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #29 / /web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #30 / /vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #31 / /web/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #32 / /web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #33 {main}.

Second log:

mailjet_messages: The new contact was added to list #10041999.

Thirdly:

Error: Call to a member function get() on null in Drupal\Core\Session\SessionHandler->write() (line 76 of / /web/core/lib/Drupal/Core/Session/SessionHandler.php) #0 / /vendor/symfony/http-foundation/Session/Storage/Handler/WriteCheckSessionHandler.php(90): Drupal\Core\Session\SessionHandler->write('LlRnGOtG2CQST9u...', '_symfony_flashe...') #1 / /web/core/lib/Drupal/Core/Session/WriteSafeSessionHandler.php(75): Symfony\Component\HttpFoundation\Session\Storage\Handler\WriteCheckSessionHandler->write('LlRnGOtG2CQST9u...', '_symfony_flashe...') #2 / /vendor/symfony/http-foundation/Session/Storage/Proxy/SessionHandlerProxy.php(67): Drupal\Core\Session\WriteSafeSessionHandler->write('LlRnGOtG2CQST9u...', '_symfony_flashe...') #3 [internal function]: Symfony\Component\HttpFoundation\Session\Storage\Proxy\SessionHandlerProxy->write('LlRnGOtG2CQST9u...', '_symfony_flashe...') #4 / /vendor/symfony/http-foundation/Session/Storage/NativeSessionStorage.php(244): session_write_close() #5 / /web/core/lib/Drupal/Core/Session/SessionManager.php(198): Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage->save() #6 / /vendor/symfony/http-foundation/Session/Session.php(197): Drupal\Core\Session\SessionManager->save() #7 / /web/core/lib/Drupal/Core/StackMiddleware/Session.php(60): Symfony\Component\HttpFoundation\Session\Session->save() #8 / /web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #9 / /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #10 / /web/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #11 / /web/modules/contrib/jsonapi/src/StackMiddleware/FormatSetter.php(41): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #12 / /web/modules/contrib/cdn/src/StackMiddleware/DuplicateContentPreventionMiddleware.php(119): Drupal\jsonapi\StackMiddleware\FormatSetter->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #13 / /web/core/modules/ban/src/BanMiddleware.php(50): Drupal\cdn\StackMiddleware\DuplicateContentPreventionMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #14 / /web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #15 / /web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #16 / /vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #17 / /web/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 / /web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #19 {main}.

Which then breaks the user upload progress.

So:
Why Mailjet thinks it is a new user in the first place?
Is there a way to turn off syncing? At least syncing user images which are not necessary when syncing email addresses to a service.