Problem description:

Our moodle platform serves 4 courses which have been generated from the same template over 2 years. Each of those has a Wiki,  amongst other  activities.

We use Nextcloud  to upload images and link those to moodle. This works flawless in 3 of 4 courses. In the second course, the images get displayed for about 20 Minutes and then disappear.

I could not find issues related to my problem. There have been some issues in the past, which were similar to what i see, but probably not the same.

Steps to reproduce:

You need moodle and one instance of Nextcloud. moodle and nextcloud need to be set up to share files via OAuth2 (needs repository_owncloud and Nextcloud Version >13)

Follow https://docs.moodle.org/36/en/Nextcloud_repository

and

https://docs.moodle.org/36/en/OAuth_2_services

1. Set up one or more moodle courses with at least one wiki-activity
2. Create a new wiki page (HTML)
3. Insert some images from your nextcloud repository, insert them as a copy / as  a direct link / as an alias-link (try all the options moodle offers)
4. Save the page you created and verify that images show
5. Reload the page after a certain amount of time (how long you might have to wait might depent on other variables, that i do not understand by now) and verify that the images are no longer there. You might see the 'alt'-Text of those images. 
6. Browser console shows a 404 - File not found error for those files affected

There are no php-errors and i  see nothing helpful in the server logs.

I would really appreciate any help!

Thanks