Portainer afaik doesn’t have an auto update function. The last time I tried it exactly like this it worked completely fine.
Edit:
I stopped the Portainer container before restarting the PMS container after running the update. Same result. It still gets downgraded. I don’t use watchtower or anything that auto updates my containers.
Edit 2:
I even tried the update from within a docker container with the “latest” and “beta” tag but it always gets downgraded. I don’t know what’s wrong. Guess I sadly can’t test this build. 
