I don't know how you are setting this but try a different approach. For example, if you are using Bar Settings for the rests, try specifying the rests with chords instead (i.e. C.bd etc.) So to rest everything but bass/drums for 4 bars do something like C.bd|Am.bd|F.bd|G.bd

For your second question, make sure the RT in question supports Holds. In the RT picker, there is a column labeled Holds. If your instrument has a number there, the hold should work.

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