You can Report Bugs from Support Section in Marvis Settings. But no need now, I've got your Report here.
Thanks a lot for Reporting the Bug.
That's Probably due to some 8.4 change, doesn't happen for me but I think I've already solved it in the Next version. I don't know what specific thing Crashes for you. Most likely it won't crash in Next Version.
I'll submit the v2.2 tomorrow, and it'll be available after a week or so.
It's Mavis itself that crashes and closes itself. Not sure what, but I guess I'll wait for the next build. Just figured I'd let you know! I'll check whenever it updates and let you know if it persists.