What does "Reverted from vX to vY" means

I am confused by how Fly visualizes releases. What release is running?

Release

Reverted from v4 to v6

Release

Released v5

Release

Released v4

Er … yes that console output is indeed slightly unclear. Perhaps a better view is the output of fly status. You can see each running vm for the app, with its release/version number e.g

Instances
ID      PROCESS	VERSION	REGION	DESIRED	STATUS 	HEALTH CHECKS     	RESTARTS	CREATED              
abcdefg	app    	65     	lhr   	run    	running	1 total, 1 passing	0       	2022-08-09T18:02:56Z
1 Like

So it says version 6. Does that mean that version 5 was not OK is some matter and therefore version 6 was created from version 4?

Yes, this means it rolled back version 5. Nomad (we use nomad under the covers) does this by creating a new release with the same contents as v4.