Hi Fabian,
There are two more possibilities to your issues.
1) There might be a filter to a field and the field is not available in the Displayed Columns which makes you think that there is no filter. So, I would suggest to add all the columns to the layout and see if any field is filtered with. Were you able to see all the cases before and it's not happening now?
2) Second check is with Authorisation. There might be some authorisation set by your security team to display by filtering out only cases with certain status or any other field. Try checking with your security team and see what you come with.
Thanks,
Basavaraj