The following error occured after upgrade to MW 1.35 (Linked 3.4.2), it seems popper.js is missing.
/linked/load.php?lang=en&modules=ext.LinkedWiki.SparqlParser%2Csgvizler2%7Cjquery%2Coojs-ui-core&skin=vector&version=1wkye RuntimeException from line 485 of /var/www/html/includes/resourceloader/ResourceLoaderFileModule.php: ResourceLoaderFileModule::getFileContents: script file not found, or is not a file: "/var/www/html/extensions/LinkedWiki/node_modules/popper.js/dist/umd/popper.min.js"
Backtrace:
#0 /var/www/html/includes/resourceloader/ResourceLoaderFileModule.php(905): ResourceLoaderFileModule->getFileContents(string, string)
#1 /var/www/html/includes/resourceloader/ResourceLoaderFileModule.php(362): ResourceLoaderFileModule->readScriptFiles(array)
#2 /var/www/html/includes/resourceloader/ResourceLoaderModule.php(736): ResourceLoaderFileModule->getScript(ResourceLoaderContext)
#3 /var/www/html/includes/resourceloader/ResourceLoaderModule.php(704): ResourceLoaderModule->buildContent(ResourceLoaderContext)
#4 /var/www/html/includes/resourceloader/ResourceLoader.php(1191): ResourceLoaderModule->getModuleContent(ResourceLoaderContext)
#5 /var/www/html/includes/resourceloader/ResourceLoader.php(899): ResourceLoader->makeModuleResponse(ResourceLoaderContext, array, array)
#6 /var/www/html/load.php(51): ResourceLoader->respond(ResourceLoaderContext)
#7 /var/www/html/load.php(38): wfLoadMain()
#8 {main}