The Dollar Universe Engines ( Launcher, Calculator...) cannot be Stopped or Started since the moment that the Maintenance of the Job / Resource Logs starts ( which is right before the Online Purge).
No errors are generated in the universe.log and it is unclear why this operation cannot be done.
Engines Status can only be modified after the Online Purge has finished.
If Archiving was enabled, the Engines were locked while the tar / zip command was running.
Dollar Universe 6
Update to a fix version listed below or a newer version if available.
Dollar Universe 6.10.01 - Released 30th May 2019
There will still be an Engine lock during Online Purge, but if the Job / Resource Logs are Archived, while the tar / zip command is running, Engines will no longer be Locked.