This is both for retry when, for example the backup done prior to the update, fails temporarily, as well as if apps and platform gets updates, they lock each other so retries in not so busy times are an effective workaround.
@girish Many thanks Girish. It must have been a space problem indeed. Looking at the log, the processed froze while downloading the last big part of the image (~570MB). I tried to duplicate the app, which worked fine but and the process also froze when trying to update it (also while downloading that part the image).
Anyway, I had a about 3GB of free space which I though would be enough to update Wekan but after doing some cleaning up on the server (like deleting old apps I wasn't using), I went to about 7GB of free space and the update started working again.
@ruihildt Updates to packages are rolled out slowly. So if a user tries to check for an update manually (i.e they click for 'check for updates') and they are not part of the rollout, they get shown that message. Generally, it is safe to update anyway but we are just being careful here.