Scene disappears and Dimension hangs. No crash report.

Hello

I've been working on a complex scene for a few days. Dimenbion updated this morning and now I keep getting hangs where either some objects disappear when I'm performing a function (grouping) or the whole scene disappears (during a move) and then Dimension hangs with no crash report or any other indication of an error. 

I have to use Force Quit to close the app.

Not sure what I'm supposed to try. No new objects have appeared in the scene simce the previous version (of Dimension) which seemed to be fine.