Not completely sure if my problem is the same as people previously said in this thread but my cast bars weren't appearing anymore. After trying to find a solution in this thread and disable/enable addon by addon I narrowed down the problem having something to do with SharedMedia. When having SharedMedia enable it doesn't show my cast bars and after I disabled it they appeared again. Now I have no idea on how to go fix this so if people can help me with this problem that would be appreciated :)
edit: After playing around with the MyMedia file it seems that deleting this line
local SML = AceLibrary("SharedMedia-1.0")
makes the cast bars disappear. However, when leaving this line in the file I ain't able to use MyMedia files.
edit2: Decided to try and fix it myself. Tried different stuff with the MyMedia.lua but nothing works so I copied the files to the SharedMedia folders itself instead of MyMedia and that works at least.