I am getting the following runtime warning message which happens often but not on every page:
User warning: The following theme is missing from the file system: jquery_ui_tooltip in Drupal\Core\Extension\ExtensionPathResolver->getPathname() (line 63 of /var/www/html/web/core/lib/Drupal/Core/Extension/ExtensionPathResolver.php)
#0 /var/www/html/web/core/includes/bootstrap.inc(164): _drupal_error_handler_real(512, 'The following t...', '/var/www/html/w...', 63)
#1 [internal function]: _drupal_error_handler(512, 'The following t...', '/var/www/html/w...', 63)
#2 /var/www/html/web/core/lib/Drupal/Core/Extension/ExtensionPathResolver.php(63): trigger_error('The following t...', 512)
#3 /var/www/html/web/core/lib/Drupal/Core/Extension/ExtensionPathResolver.php(85): Drupal\Core\Extension\ExtensionPathResolver->getPathname('theme', 'jquery_ui_toolt...')
#4 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php(127): Drupal\Core\Extension\ExtensionPathResolver->getPath('theme', 'jquery_ui_toolt...')
#5 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDiscoveryCollector.php(87): Drupal\Core\Asset\LibraryDiscoveryParser->buildByExtension('jquery_ui_toolt...')
#6 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDiscoveryCollector.php(66): Drupal\Core\Asset\LibraryDiscoveryCollector->getLibraryDefinitions('jquery_ui_toolt...')
#7 /var/www/html/web/core/lib/Drupal/Core/Cache/CacheCollector.php(149): Drupal\Core\Asset\LibraryDiscoveryCollector->resolveCacheMiss('jquery_ui_toolt...')
#8 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDiscovery.php(44): Drupal\Core\Cache\CacheCollector->get('jquery_ui_toolt...')
#9 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDiscovery.php(58): Drupal\Core\Asset\LibraryDiscovery->getLibrariesByExtension('jquery_ui_toolt...')
#10 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(68): Drupal\Core\Asset\LibraryDiscovery->getLibraryByName('jquery_ui_toolt...', 'tooltip')
#11 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(70): Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies(Array, Array)
#12 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(41): Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies(Array)
#13 /var/www/html/web/core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php(87): Drupal\Core\Asset\LibraryDependencyResolver->getLibrariesWithDependencies(Array)
#14 /var/www/html/web/core/lib/Drupal/Core/Asset/AssetResolver.php(113): Drupal\Core\Asset\LibraryDependencyResolver->getMinimalRepresentativeSubset(Array)
#15 /var/www/html/web/core/lib/Drupal/Core/Asset/AssetResolver.php(131): Drupal\Core\Asset\AssetResolver->getLibrariesToLoad(Object(Drupal\Core\Asset\AttachedAssets))
#16 /var/www/html/web/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(321): Drupal\Core\Asset\AssetResolver->getCssAssets(Object(Drupal\Core\Asset\AttachedAssets), true, Object(Drupal\Core\Language\Language))
#17 /var/www/html/web/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(165): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAssetLibraries(Object(Drupal\Core\Asset\AttachedAssets), Array)
#18 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipeResponseAttachmentsProcessor.php(97): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#19 /var/www/html/web/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php(45): Drupal\big_pipe\Render\BigPipeResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#20 [internal function]: Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#21 /var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher))
#22 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(214): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response')
#23 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(202): Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object(Drupal\Core\Render\HtmlResponse), Object(Symfony\Component\HttpFoundation\Request), 1)
#24 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(76): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#25 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/Session.php(58): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#26 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#27 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ContentLength.php(28): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#28 /var/www/html/web/core/modules/big_pipe/src/StackMiddleware/ContentLength.php(32): Drupal\Core\StackMiddleware\ContentLength->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#29 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\big_pipe\StackMiddleware\ContentLength->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#30 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#31 /var/www/html/web/core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#32 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(48): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#33 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(51): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#34 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/AjaxPageState.php(36): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#35 /var/www/html/web/modules/contrib/remove_http_headers/src/StackMiddleware/RemoveHttpHeadersMiddleware.php(49): Drupal\Core\StackMiddleware\AjaxPageState->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#36 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php(51): Drupal\remove_http_headers\StackMiddleware\RemoveHttpHeadersMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#37 /var/www/html/web/core/lib/Drupal/Core/DrupalKernel.php(704): Drupal\Core\StackMiddleware\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#38 /var/www/html/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#39 {main}
This error happens often but not all the time so I'm not quite sure how to reproduce it. Also oddly the jQuery UI Tooltip module is not enabled (see attached image) so I don't know why it should throw this warning...or perhaps that's the problem?