One workaround I found is to re-parent all the BPs that you want to migrate to a more generic class that’s inherent in the editor (e.g. Pawn, Actor). Then migrate the asset, and then re-parent it back to its original c++ parent class. (This assumes you successfully transferred and compiled all your c++ code to the new project.) If you do this, I highly recommend you do it from a copy of the project from which you want to migrate, not the project itself. This will break a lot of stuff.
This is a very crude work-around. Depending on the Blueprint, it requires extensively going through that blueprint and fixing a lot of the errors that occur from the re-parenting, resetting defaults, etc. It’s quite a hassle, and it cost me a lot of time. I don’t think this “solution” is deserving of an acceptance tick. I await a more elegant solution. If there doesn’t exist one, then perhaps this should prompt a requested feature.