Domain guards - applied one and it disappears almost immediately
So, I killed a Longobard Uber and sent some troops to farm it for an hour. Applied a 1 hour Domain Guard on it. No troops were recalled.
Noticed a few minutes later that the Domain Guard was gone. I quickly restarted the game and found it wasn't a glitch on my side and applied another Domain Guard before somebody killed my troops.
Domain Guards are not easily to get (unless you buy them) - so I only use them when in CVC & KVK events.
Question: Why would a a Domain Guard expire/disappear within a couple of minutes?
Using latest version of FireFox on PC.