I've been using the popular Keychain mod for ages, and had over 100 hours of playtime logged on this character with no keychain issues... until today.

Not sure if the location is relevant but it was at Fathis Ules' Tower on the Thieve's Guild questline. I found Ules' key, required for exiting the tower, and then 'interacted' with a nearby chest to bring up the lockpick menu. Suddenly a message popped up regarding the Keychain mod saying something about using a 'no key' method (perhaps an advanced option of the mod?) and that it's a bad thing to use. It said that if I exited the lockpick interface then the lockpick interface would reload, and seemed to suggest that I should avoid that. Well, I was already in the interface so I HAD to exit at some point, and sure enough it reloaded. Seemed fine until I exited again and checked my inventory.

No Keychain.

No keys.

The mod stopped working and for some reason thought the best course of action would be to delete all those keys I owned, including the unique ones. Yay!

I'm wondering if this is a common problem and if there's a way to fix it? Presumably I can always delete this mod and add each key back in to my inventory using the console, but that just sounds... exhausting.

Thanks for reading ^_^

Did you restart the game and see if it was there?

Try the command given in the readme "StartQuest P1DkeyAdd"?