I think it would be good to test again using the latest 8.3 Release Candidate and let us know if the problem persists. I say this because we recently fixed:
RH-69542 Panels: Floating a container outside of virtual desktop causes container to disappear on Mac
in 8.3 and it feels related, but we can’t be sure unless until you let us know (since we can’t seem to reproduce this behavior here).