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.
I'm not stopping there, More Coming soon.