just in case someone else is doing backups like me by copying and refreshing containers, I opened a ticket on github (https://github.com/lxc/lxd/issues/5708) since on my install it removes the uid/gid mappings from the backupped container configuration and so processes won’t start due to wrong mappings.
Just copying the container (without --refresh) works fine.
Maybe there’s something wrong with my backup strategy, but still I feel this is a bug…eh strange feature I mean
I am using snap 3.12 v10601 on ubuntu 18.04 and 18.10