After playing a bit in Devotion Garden and having several turrets upgraded, I saved the game and quit. After a short break I loaded the game only to discover that all turrets were back to their basic state.

To clarify: I do not mean any turret research. I mean turrets that I could and did upgrade after they got enoug experience (or whatever the mechanic is called).

TowerUpgradesLost.7z

Thank you for the report! This issue was not known before and has been added to our list of bugs.