Can't mount during refresh - installation not allowed by plug rule

snapcraft
1

I have a custom snap in a custom brand store. When I run snap refresh it sometimes fails and returns this message:

$ snap refresh
error: cannot perform the following tasks:
- Mount snap "deel-cl2-device-agent" (49) (installation not allowed by "shutdown" plug rule of interface "shutdown")

This hasn’t happened with previous revisions and we haven’t changed anything with the plugs / interfaces that I’m aware of. The shutdown plug is connected by our gadget:

[deeladmin@wide-eyed-acoustics-cl2 ~]$ snap connections deel-cl2-device-agent | grep shutdown
shutdown                deel-cl2-device-agent:shutdown               :shutdown                              gadget

I have tried rebooting, retrying the refresh and disconnecting and reconnecting the plug manually but none of those worked. On SOME devices I can update to this revision fine.

What should I check next?

Thanks Jeremy