Update: I found multiple empty files in the wire folder.
After i reuploaded the wire folder two days ago through the console, i didn´t check if every file was uploaded correctly.
I opened the first file mentioned in the error and it was empty, so i uploaded it manually and repeated that process for 7 more files.
Now everything seems to work fine.
I have absolutely no idea why or how this can happen, nor the correlation to the Core Update. Seems really strange.
Anyway, thank you guys for your replies!