If you're using Rotobrush you have to know how to use it and freeze it when the Roto is complete or you'll have a mess.
In most cases if my Roto is more than just a few frames I will render the Roto to a 10 bit or better lossless format and replace the layer in the comp. I call that making a DI. The output module has a renter and replace option.
Make sure you thoroughly understand the proper use and workflow for Rotobrush.