Internal Server Error -> While opening document in shared folder

Hi!
I have configured a folder so that customers can edit doc-files remotely via Collabora. This worked pretty well. I tried it yesterday.
Now a customer tried to open the doc file and he see this. I can confirm that I am also not able to open it anymore-
I was able to edit this file. Now I see

Interner Serverfehler
Der Server hat einen internen Fehler und konnte Ihre Anfrage nicht vervollständigen.
Bitte wenden Sie sich an den Serveradministrator, wenn dieser Fehler mehrfach auftritt, geben Sie bitte die,
unten stehenden, technischen Details in Ihrem Bericht mit an.
Weitere Details können im Server-Protokoll gefunden werden.

In the logs I can see following:

{"reqId":"mK2NEUqmuxt1KvunkJhM","remoteAddr":"***.***.***.***","app":"index","message":"Exception: {\"Exception\":\"Error\",\"Message\":\"Call to a member function getUID() on null\",\"Code\":0,\"Trace\":\"#0 \\\/var\\\/www\\\/nextcloud\\\/apps\\\/richdocuments\\\/lib\\\/Controller\\\/DocumentController.php(153): OCA\\\\Richdocuments\\\\TokenManager->getToken(*** sensitive parameters replaced ***)\\n#1 [internal function]: OCA\\\\Richdocuments\\\\Controller\\\\DocumentController->publicPage('HjdvgD72JFT9FPU', 'NAME...')\\n#2 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(160): call_user_func_array(Array, Array)\\n#3 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(90): OC\\\\AppFramework\\\\Http\\\\Dispatcher->executeController(Object(OCA\\\\Richdocuments\\\\Controller\\\\DocumentController), 'publicPage')\\n#4 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/App.php(114): OC\\\\AppFramework\\\\Http\\\\Dispatcher->dispatch(Object(OCA\\\\Richdocuments\\\\Controller\\\\DocumentController), 'publicPage')\\n#5 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/AppFramework\\\/Routing\\\/RouteActionHandler.php(47): OC\\\\AppFramework\\\\App::main('OCA\\\\\\\\Richdocumen...', 'publicPage', Object(OC\\\\AppFramework\\\\DependencyInjection\\\\DIContainer), Array)\\n#6 [internal function]: OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler->__invoke(Array)\\n#7 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/private\\\/Route\\\/Router.php(299): call_user_func(Object(OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler), Array)\\n#8 \\\/var\\\/www\\\/nextcloud\\\/lib\\\/base.php(1010): OC\\\\Route\\\\Router->match('\\\/apps\\\/richdocum...')\\n#9 \\\/var\\\/www\\\/nextcloud\\\/index.php(40): OC::handleRequest()\\n#10 {main}\",\"File\":\"\\\/var\\\/www\\\/nextcloud\\\/apps\\\/richdocuments\\\/lib\\\/TokenManager.php\",\"Line\":93}","level":3,"time":"2017-01-18T11:52:36+00:00","method":"GET","url":"\/index.php\/apps\/richdocuments\/public?shareToken=HjdvgD72JFT9FPU&fileName=NAME-Q%26A.DOCX&requesttoken=csHiVmQgvnK09RfdxfSRKP9R7lELCrWNyaJeyN%2FX3tA%3D%3ANpPTGBJhxB7uhDiLibXofa0itws6b9%2FKnMU6kJO0h%2Fs%3D","user":"--","version":"11.0.1.2"}

Does anyone know what this the cause for this issue? Any help is appreciated.

Maybe this info is helpful to find the trouble maker.

Oh, I forgot to mention that the document is hosted on a external smb-drive, that is mounted via NC.

I think I am having the same error here:

Remote Address: 2a02:8109:a4bf:fe85:3ea9:f4ff:fe33:20a4
Request ID: Ef1Z8fTayt6pfmIOZseT
Type: Error
Code: 0
Message: Call to a member function getUID() on null
File: /srv/www/htdocs/nextcloud/apps/richdocuments/lib/TokenManager.php
Line: 93

Trace
#0 /srv/www/htdocs/nextcloud/apps/richdocuments/lib/Controller/DocumentController.php(103): OCA\Richdocuments\TokenManager->getToken(3613264)
#1 [internal function]: OCA\Richdocuments\Controller\DocumentController->index('3613264_/')
#2 /srv/www/htdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php(160): call_user_func_array(Array, Array)
#3 /srv/www/htdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php(90): OC\AppFramework\Http\Dispatcher->executeController(Object(OCA\Richdocuments\Controller\DocumentController), 'index')
#4 /srv/www/htdocs/nextcloud/lib/private/AppFramework/App.php(114): OC\AppFramework\Http\Dispatcher->dispatch(Object(OCA\Richdocuments\Controller\DocumentController), 'index')
#5 /srv/www/htdocs/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php(47): OC\AppFramework\App::main('OCA\\Richdocumen...', 'index', Object(OC\AppFramework\DependencyInjection\DIContainer), Array)
#6 [internal function]: OC\AppFramework\Routing\RouteActionHandler->__invoke(Array)
#7 /srv/www/htdocs/nextcloud/lib/private/Route/Router.php(299): call_user_func(Object(OC\AppFramework\Routing\RouteActionHandler), Array)
#8 /srv/www/htdocs/nextcloud/lib/base.php(1010): OC\Route\Router->match('/apps/richdocum...')
#9 /srv/www/htdocs/nextcloud/index.php(40): OC::handleRequest()
#10 {main}

My doc is just on internal storage.

Error in the javascript console:

Failed to load resource: the server responded with a status of 500 (Internal Server Error)
jquery-migrate.min.js:2 JQMIGRATE: Migrate is installed, version 1.4.0
shareconfigmodel.js:24 Uncaught ReferenceError: oc_appconfig is not defined
    at shareconfigmodel.js:24
    at shareconfigmodel.js:77
js.js:201 Uncaught TypeError: Cannot read property 'substring' of undefined
    at Object.filePath (js.js:201)
    at viewer.js:15

This happens with a file shared with me.

When I try to open a file that I own and created, I get a rather simple “access forbidden”!

EDIT:
Trying to reach the URL I have configured Collabora to run on, I get a access forbidden in my browser, too: it seems my certificate expired! So that is probably the reason. Now trying to fix that…