Problems with changing the instruments

In my piece some parts of string instruments should be notate on 1-line staff. I made two instruments for every player to do that. Unfortunately, in some cases the score shows two instruments at once (even if the second have only rests).
I tried removing staves and it works, but when I do that, all stave is removed in all pieces so that I can’t then return to 5-line staff:/
Do you have any ideas?

No chance to say, why it sometimes works and sometimes doesn’t.
A stripped down project, where everyone can take a look may help.

If instrument changes are allowed in the layout, you should see the player switching between their pitched and unpitched instruments in the same “staff”, provided that there is no overlapping material at any point between the two instruments in that system.

If you can’t see an obvious overlap, then you will need to share the project for someone to look into what’s going on, as this cannot be diagnosed from a description alone.

I’ve just remove and add the 5-line violini again, and now everything is working. Thank you very much for responses.