Looking in the lxd source code I found out error message:
$ rg "running operations can be connected" lxd/operations/operations.go 426: return nil, fmt.Errorf("Only running operations can be connected")
Looking in the lxd source code I found out error message:
$ rg "running operations can be connected" operations. go
lxd/operations/
426: return nil, fmt.Errorf("Only running operations can be connected")