Apart from the obvious (your def getting killed), there are plenty of other reasons for that to happen: some item expired, prestige expired, you reshuffled relics, you played with active potions, your Bastion got downgraded,...

If you still feel it's a glitch and not one or more of what I've listed (or maybe something I've forgotten), please either provide your ID (the bottom left of the Help window) or specify which platform (Plarium (app included) or FB) and coordinates you're playing at, so the techs can try to take a look.

Thank you for that answer, I just noticed that I had handled relics. 

I'm happy we resolved it quickly. 

The game has (too?) many factors and it's easy to miss something. I almost forgot potions when I was writing the above.