Thank you very much Marcel!
There was indeed an issue, and interestingly it was not due to the existend of the cache folder, it was much more complex – it took me 3 hours to investigate.
Basically what happend is, that for some reason the search override triggered so many times, that a certain function caused a memory limit problem, the process ran out of memory, and halted. It caused no further issues, but was super hard to find.
I needed to edit multiple files in the plugin to bypass the problem, it should work all right now. This is going to be permanently fixed in the upcoming patch of course.