Undefined offset: 1

Problem/Motivation

I upgraded my development site from b5 to b6.

when displaying a test page, I get this error (about 40 times)

Notice: Undefined offset: 1 in Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies() (line 53 of .../core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php)
#0 .../core/includes/bootstrap.inc(600): _drupal_error_handler_real(8, 'Undefined offse...', '/home3/rvuufian...', 53, Array)
#1 .../core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(53): _drupal_error_handler(8, 'Undefined offse...', '/home3/rvuufian...', 53, Array)
#2 .../core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(31): Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies(Array)
#3 .../core/lib/Drupal/Core/Asset/AssetResolver.php(104): Drupal\Core\Asset\LibraryDependencyResolver->getLibrariesWithDependencies(Array)
#4 .../core/lib/Drupal/Core/Asset/AssetResolver.php(116): Drupal\Core\Asset\AssetResolver->getLibrariesToLoad(Object(Drupal\Core\Asset\AttachedAssets))
#5 .../core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(315): Drupal\Core\Asset\AssetResolver->getCssAssets(Object(Drupal\Core\Asset\AttachedAssets), true)
#6 .../core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(161): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAssetLibraries(Object(Drupal\Core\Asset\AttachedAssets), Array)
#7 .../core/modules/big_pipe/src/Render/BigPipeResponseAttachmentsProcessor.php(94): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#8 .../core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php(45): Drupal\big_pipe\Render\BigPipeResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#9 [internal function]: Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond(Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#10 .../core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#11 .../vendor/symfony/http-kernel/HttpKernel.php(191): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.response', Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent))
#12 .../vendor/symfony/http-kernel/HttpKernel.php(173): Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object(Drupal\Core\Render\HtmlResponse), Object(Symfony\Component\HttpFoundation\Request), 1)
#13 .../vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#14 .../core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#15 .../core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#16 .../core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#17 .../core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#18 .../core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#19 .../core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#20 .../core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#21 .../vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#22 .../core/lib/Drupal/Core/DrupalKernel.php(708): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#23 .../index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#24 {main}

Steps to reproduce

here's the page from my production site (running b5) -- it's fine
https://communicrossings.com/drupal-crossword-example-olli

same page on my development site w/ b6 generates the errors

early on I thought I salso aw an error message regarding a (missing) font -- but not seeing that now

Steve