vst plugins not working on some tracks

lately, the following strange behaviour has come up in Cubase:
in some projects, many plugins do not respond to the audio. They just sit in the track and do nothing.
But when I move them to the master output track, they work.
At first I thought that it might be a vst3 or vst2 issue, but the problem appears with both types.

I can’t seem to figure out what the problem is.

Cubase 9.5 (latest version), windows 10 (also latest version), UR824

update: these tracks were imported from a multichannel audio file (8ch)
When I create new tracks, and move the audio there, the plugins work.
Problem (sort of) solved, but still no idea why this happens.