Call to undefined method AccountProxy::getUsername()

I have already applied https://www.drupal.org/project/disqus/issues/3143716 - however that only seems to change the .info.yml file...

The error I get is this:

The website encountered an unexpected error. Please try again later.
Error: Call to undefined method Drupal\Core\Session\AccountProxy::getUsername() in Drupal\disqus\Element\Disqus::displayDisqusComments() (line 83 of modules/contrib/disqus/src/Element/Disqus.php).
Drupal\disqus\Element\Disqus::displayDisqusComments('Homebrew: List packages and what uses them', 'https://tmj-tmj-d8.local.EXAMPLE.com/blog/22-09-2014/homebrew-list-packages-and-what-uses-them', 'node/427')
call_user_func_array(Array, Array) (Line: 100)
Drupal\Core\Render\Renderer->doTrustedCallback(Array, Array, 'Render #lazy_builder callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was %s. See https://www.drupal.org/node/2966725', 'exception', 'Drupal\Core\Render\Element\RenderCallbackInterface') (Line: 781)
Drupal\Core\Render\Renderer->doCallback('#lazy_builder', Array, Array) (Line: 355)
Drupal\Core\Render\Renderer->doRender(Array, 1) (Line: 200)
Drupal\Core\Render\Renderer->render(Array, 1) (Line: 156)
Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 157)
Drupal\Core\Render\Renderer->renderPlain(Array) (Line: 171)
Drupal\Core\Render\Renderer->renderPlaceholder('', Array) (Line: 658)
Drupal\Core\Render\Renderer->replacePlaceholders(Array) (Line: 543)
Drupal\Core\Render\Renderer->doRender(Array, 1) (Line: 200)
Drupal\Core\Render\Renderer->render(Array, 1) (Line: 144)
Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 145)
Drupal\Core\Render\Renderer->renderRoot(Array) (Line: 282)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->renderPlaceholders(Object) (Line: 131)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments(Object) (Line: 45)
Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond(Object, 'kernel.response', Object) (Line: 78)
Symfony\Component\EventDispatcher\LegacyEventDispatcherProxy->dispatch(Object, 'kernel.response') (Line: 191)
Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object, Object, 1) (Line: 179)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 705)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)