In my SE playthrough the trains "forget" their next stop and restart their schedule after landing, instead of continuing to the current stop.
Am i missing something?

By default train schedules advance one station after jumping off a ramp but you can press F on the ramp to toggle that on and off. If the train is in the last stop on the schedule then advancing one stop would then loop it back to the first one, but if that's not the case then I don't know why that would be happening. Can you upload your save file somewhere I can take a took?

Oh, havent seen that option anywhere - that could solve it already.
will report if its not helping, thanks.

update:
in fact it was the "skip next stop behaviour".
The blue ramps (after pressing F) work fine, thanks.

An idea that popped up: is it possible for a train to BLOCK the railsignal/block it will land on while beeing in the air? i Found that not blocking leads to collisions when another train comes up to that railblock while the aired train is landing...

The train system is pretty locked down in the API as far as I can tell so it would be tricky to toggle rail signals reliably. In theory I could spawn an invisible train in the block the jumping train will land in and then delete it when it lands, but I dont know how that would interact for other trains already in the block when the train jumps.

well, you COULD block the ramp when the destination block is yellow / red, and spawn this train when it is green and the block with the ramp is yellow / train is flying.
(for sure just working with magnetic ramps - but it would be worth it, i think, since it would lead to being able to use the ramps reliable on crossings without complicated circuits