some content on our site has different permissions and can be show via a seperate view.

But when click that view there is an error:

Sorry, something went wrong

The attempted operation is prohibited because it exceeds the list view threshold enforced by the administrator.

Microsoft support gives as reason that the library het exceed the 5000 listed files ?

Because we started this library in november 2012 with already 8500 files it was never be a problem.

Another libray which is also 8100 files listed has no problem with access and see or modify the permissions !!!