(1) After closing ONYX it fails to reopen.
(2) After leaving ONYX open all night it is slow to react to commands, if at all. Takes a reboot to get ONYX back to full operation.
I have checked memory RAM and HDD, there is plenty left.
Anyone got any suggestions?
what version #?
Build 4.8.1244.0
I’ve experienced this issue with Onyx PC for several builds, including the most recent 4.9 release candidate, on various computers. I find that the majority of the time, closing Onyx doesn’t stop all related processes and, thus, the application isn’t fully “closed” (thereby preventing Windows from re-opening it). Try taking a look at your Task Manager the next time this occurs. In my experience, there’s usually a few Onyx and Dylos-related processes that are still running. Manually killing these processes allows Onyx to be re-opened.
I had the same issues and use the TASK MANAGER to force closing and then it runs.
+1
Tried this with little success. Do you remember which ONYX or Dylos files or services I should look for in the Task Manager?
Off the top of my head, no 
But I recall their names all starting with Onyx and / or Dylos. Be sure to look under the “processes” tab in Task Manager if you aren’t already doing that. Based on the response to this thread, it seems to be a common issue - hopefully something that the devs will resolve one of these days.
On a PC, as a workaround I use Microsoft PC Manager to End Onyx processes. Then I can relaunch it without having to restart a computer.
PC Manager > Apps > Process management