using image sequence crashes

[Selur]

It might be due to the vapoursynth thing, I never managed to get it to work on my computer back when I wanted to run some scripts months ago,

That is why I asked:

Does the Vapoursynth Preview work properly?

The Vapoursynth Preview should show additional error messages, in case something doesn't work.

Also Hybrid does come with it's own portable Vapoursynth version, so unless you still got a broken install on your system there should be no problem.
-> make sure to uninstall any old/broken Vapoursynth stuff from your system.

is there an avisynth alternative or something?

Sure you can use Avisynth instead of Vapoursynth. (change "Filtering->Support" to 'Avisynth')
Just using FFmpeg and not using Avisynth or Vapoursynth (change "Filtering->Support" to ' No XSynth') should also work. (Progress indication will probably be wrong, but it should work.

Cu Selur