MediaWiki internal error.

Original exception: [42610fbff75e985ee95e9b74] /index.php?title=Spezial:Gruppenrechte Exception from line 15 of /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/PropGuard.php: Property "attrs" on object of class RemexHtml\Serializer\SerializerNode is undeclared
Backtrace:
#0 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Serializer/SerializerNode.php(53): RemexHtml\Serializer\SerializerNode->__set()
#1 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Serializer/Serializer.php(111): RemexHtml\Serializer\SerializerNode->__construct()
#2 /var/www/mantopedia.de/includes/tidy/RemexCompatMunger.php(123): RemexHtml\Serializer\Serializer->startDocument()
#3 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/TreeBuilder/TreeBuilder.php(169): MediaWiki\Tidy\RemexCompatMunger->startDocument()
#4 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/TreeBuilder/Dispatcher.php(345): RemexHtml\TreeBuilder\TreeBuilder->startDocument()
#5 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Tokenizer/Tokenizer.php(173): RemexHtml\TreeBuilder\Dispatcher->startDocument()
#6 /var/www/mantopedia.de/includes/tidy/RemexDriver.php(67): RemexHtml\Tokenizer\Tokenizer->execute()
#7 /var/www/mantopedia.de/includes/parser/MWTidy.php(48): MediaWiki\Tidy\RemexDriver->tidy()
#8 /var/www/mantopedia.de/includes/parser/Parser.php(1584): MWTidy::tidy()
#9 /var/www/mantopedia.de/includes/parser/Parser.php(596): Parser->internalParseHalfParsed()
#10 /var/www/mantopedia.de/includes/OutputPage.php(2113): Parser->parse()
#11 /var/www/mantopedia.de/includes/OutputPage.php(1835): OutputPage->parseInternal()
#12 /var/www/mantopedia.de/includes/OutputPage.php(1766): OutputPage->addWikiTextTitleInternal()
#13 /var/www/mantopedia.de/includes/OutputPage.php(4006): OutputPage->addWikiTextAsInterface()
#14 /var/www/mantopedia.de/includes/specialpage/SpecialPage.php(648): OutputPage->wrapWikiMsg()
#15 /var/www/mantopedia.de/includes/specials/SpecialListGroupRights.php(44): SpecialPage->outputHeader()
#16 /var/www/mantopedia.de/includes/specialpage/SpecialPage.php(575): SpecialListGroupRights->execute()
#17 /var/www/mantopedia.de/includes/specialpage/SpecialPageFactory.php(611): SpecialPage->run()
#18 /var/www/mantopedia.de/includes/MediaWiki.php(296): MediaWiki\Special\SpecialPageFactory->executePath()
#19 /var/www/mantopedia.de/includes/MediaWiki.php(900): MediaWiki->performRequest()
#20 /var/www/mantopedia.de/includes/MediaWiki.php(527): MediaWiki->main()
#21 /var/www/mantopedia.de/index.php(44): MediaWiki->run()
#22 {main}

Exception caught inside exception handler: [42610fbff75e985ee95e9b74] /index.php?title=Spezial:Gruppenrechte Exception from line 15 of /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/PropGuard.php: Property "attrs" on object of class RemexHtml\Serializer\SerializerNode is undeclared
Backtrace:
#0 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Serializer/SerializerNode.php(53): RemexHtml\Serializer\SerializerNode->__set()
#1 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Serializer/Serializer.php(111): RemexHtml\Serializer\SerializerNode->__construct()
#2 /var/www/mantopedia.de/includes/tidy/RemexCompatMunger.php(123): RemexHtml\Serializer\Serializer->startDocument()
#3 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/TreeBuilder/TreeBuilder.php(169): MediaWiki\Tidy\RemexCompatMunger->startDocument()
#4 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/TreeBuilder/Dispatcher.php(345): RemexHtml\TreeBuilder\TreeBuilder->startDocument()
#5 /var/www/mantopedia.de/vendor/wikimedia/remex-html/RemexHtml/Tokenizer/Tokenizer.php(173): RemexHtml\TreeBuilder\Dispatcher->startDocument()
#6 /var/www/mantopedia.de/includes/tidy/RemexDriver.php(67): RemexHtml\Tokenizer\Tokenizer->execute()
#7 /var/www/mantopedia.de/includes/parser/MWTidy.php(48): MediaWiki\Tidy\RemexDriver->tidy()
#8 /var/www/mantopedia.de/includes/parser/Parser.php(1584): MWTidy::tidy()
#9 /var/www/mantopedia.de/includes/parser/Parser.php(596): Parser->internalParseHalfParsed()
#10 /var/www/mantopedia.de/includes/cache/MessageCache.php(1243): Parser->parse()
#11 /var/www/mantopedia.de/includes/language/Message.php(1251): MessageCache->parse()
#12 /var/www/mantopedia.de/includes/language/Message.php(879): Message->parseText()
#13 /var/www/mantopedia.de/includes/language/Message.php(932): Message->toString()
#14 /var/www/mantopedia.de/includes/skins/Skin.php(720): Message->parse()
#15 /var/www/mantopedia.de/includes/skins/SkinTemplate.php(433): Skin->printSource()
#16 /var/www/mantopedia.de/includes/skins/SkinTemplate.php(215): SkinTemplate->prepareQuickTemplate()
#17 /var/www/mantopedia.de/includes/OutputPage.php(2574): SkinTemplate->outputPage()
#18 /var/www/mantopedia.de/includes/exception/MWExceptionRenderer.php(134): OutputPage->output()
#19 /var/www/mantopedia.de/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML()
#20 /var/www/mantopedia.de/includes/exception/MWExceptionHandler.php(121): MWExceptionRenderer::output()
#21 /var/www/mantopedia.de/includes/exception/MWExceptionHandler.php(195): MWExceptionHandler::report()
#22 /var/www/mantopedia.de/includes/MediaWiki.php(558): MWExceptionHandler::handleException()
#23 /var/www/mantopedia.de/index.php(44): MediaWiki->run()
#24 {main}