After 8.2 patch I got:
Interface action failed because of an AddOn
When open missions report menu when in combat. Disabling GarrisonCommander is resolves that issue, all other addons is fine.

No lua errors btw.

I have 3.1.1 version.

if by "fix it" you mean that the report still cant be open but no longer an error message appear, then the fix is on the way :)

Man, it's Blizzard. Addons are not allowed to do everything Blizzard code can do.
When in combat I cant inteerfere with blizzard things, so while in combat you can only see the current zone report

Hunting taint issues is very hard and, honestly, I dont feel that GarrisonCommander is intended to be used while fighting, nevertheless I could use some more info, like
How did you open mission report? AFAIK the button on minimap opens mission report from the very last garrison like setting (Champions,righe now).

Feature has been (maybe temporary) removed from Garrison Commander. You need to enable Garrison Commander Broker (which is bundled with Garrison Commander) to have it