InvalidArgumentException for every new LDAP User

PHP 5.6.28
mysql 5.5.53
Debian 4.7.8-1~bpo8+1

system is set up with about 500 AD-Users. I see this error logged every time an AD-user logs in for the first time.
they have no problems using nextcloud they told me of or I can see.
has someone seen something similar?

{"reqId":"IYY6qvlz6bJsrMxrosmd","remoteAddr":"10.10.1.201","app":"no app in context","message":"Exception:{\"Exception\":\"InvalidArgumentException\",\"Message\":\"The given object name is invalid\",\"Code\":0,\"Trace\":\"
#0 \\\/var\\\/www\\\/nextcloud\\\/apps\\\/activity\\\/lib\\\/FilesHooks.php(892): OC\\\\Activity\\\\Event->setObject('files', 41632, false)\\n
#1 \\\/var\\\/www\\\/nextcloud\\\/apps\\\/activity\\\/lib\\\/FilesHooks.php(184): OCA\\\\Activity\\\\FilesHooks->addNotificationsForUser('someLDAPuser', 'created_self', Array, 41632, false, true, true, 0, 'file_created')\\n
#2 \\\/var\\\/www\\\/nextcloud\\\/apps\\\/activity\\\/lib\\\/FilesHooks.php(111): OCA\\\\Activity\\\\FilesHooks->addNotificationsForFileAction('\\\/', 'file_created', 'created_self', 'created_by')\\n
#3 \\\/var\\\/www\\\/nextcloud\\\/apps\\\/activity\\\/lib\\\/FilesHooksStatic.php(45): OCA\\\\Activity\\\\FilesHooks->fileCreate('\\\/')\\n
#4 [internal function]: OCA\\\\Activity\\\\FilesHooksStatic::fileCreate(Array)\\n
#5 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/legacy\\\/hook.php(106): call_user_func(Array, Array)\\n
#6 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/View.php(1237): OC_Hook::emit('OC_Filesystem', 'post_create', Array)\\n
#7 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/View.php(1163): OC\\\\Files\\\\View->runHooks(Array, '\\\/someLDAPuser\\\/fi...', true)\\n
#8 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/View.php(266): OC\\\\Files\\\\View->basicOperation('mkdir', '\\\/someLDAPuser\\\/fi...', Array)\\n
#9 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/Node\\\/Folder.php(149): OC\\\\Files\\\\View->mkdir('\\\/someLDAPuser\\\/fi...')\\n
#10 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/Node\\\/Root.php(380): OC\\\\Files\\\\Node\\\\Folder->newFolder('\\\/someLDAPuser\\\/fi...')\\n
#11 [internal function]: OC\\\\Files\\\\Node\\\\Root->getUserFolder('someLDAPuser')\\n
#12 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/Node\\\/LazyRoot.php(65): call_user_func_array(Array, Array)\\n
#13 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Files\\\/Node\\\/LazyRoot.php(282): OC\\\\Files\\\\Node\\\\LazyRoot->__call('getUserFolder', Array)\\n
#14 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Server.php(948): OC\\\\Files\\\\Node\\\\LazyRoot->getUserFolder('someLDAPuser')\\n
#15 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/User\\\/Session.php(411): OC\\\\Server->getUserFolder('someLDAPuser')\\n
#16 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/User\\\/Session.php(479): OC\\\\User\\\\Session->prepareUserLogin(true)\\n
#17 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/User\\\/Session.php(299): OC\\\\User\\\\Session->loginWithPassword(*** sensitive parameters replaced ***)\\n
#18 \\\/var\\\/www\\\/nextcloud\\\/core\\\/Controller\\\/LoginController.php(244): OC\\\\User\\\\Session->login(*** sensitive parameters replaced ***)\\n
#19 [internal function]: OC\\\\Core\\\\Controller\\\\LoginController->tryLogin(*** sensitive parameters replaced ***)\\n
#20 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(160): call_user_func_array(Array, Array)\\n
#21 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(90): OC\\\\AppFramework\\\\Http\\\\Dispatcher->executeController(Object(OC\\\\Core\\\\Controller\\\\LoginController), 'tryLogin')\\n
#22 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/App.php(114): OC\\\\AppFramework\\\\Http\\\\Dispatcher->dispatch(Object(OC\\\\Core\\\\Controller\\\\LoginController), 'tryLogin')\\n
#23 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Routing\\\/RouteActionHandler.php(47): OC\\\\AppFramework\\\\App::main('LoginController', 'tryLogin', Object(OC\\\\AppFramework\\\\DependencyInjection\\\\DIContainer), Array)\\n
#24 [internal function]: OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler->__invoke(Array)\\n
#25 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Route\\\/Router.php(299): call_user_func(Object(OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler), Array)\\n
#26 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/base.php(1010): OC\\\\Route\\\\Router->match('\\\/login')\\n
#27 \\\/var\\\/www\\\/nextcloud\\\/index.php(40): OC::handleRequest()\\n
#28 {main}\",\"File\":\"\\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Activity\\\/Event.php\",\"Line\":401}","level":3,"time":"2017-01-24T09:54:19+00:00","method":"POST","url":"\/index.php\/login","user":"someLDAPuser","version":"11.0.0.10"}