This is a known problem that must be fixed in the next update. BorisFX (Owner of Mocha) has some solutions in their website but even with Mocha VR you cannot copy and paste mocha masks. Transferring transform data or corner pin data should work with CC2018, the problem is only with masks.
What I suggest you is to install AE CC 2017.2 (14.2) if you need to transfer masks from mocha to AE. With CC 2018 it does not work.