Right now im not really sure where exactly the issue lies.
I already disabled a bunch of mods and tried to narrow it down, but i have not found it yet.
Perhapse someone of you already recognized this and found a solution.
- Materials are not further moving on the belts
- as soon as you change something (orientation, reconstruct, etc) on that belt or a neigbour belt, everything works again
In the following gif, you can see the behaviour (savegame is attached):


