We aren’t perfect so don’t be hard on yourself
Hopefully it is something simple that can be fixed
The feed is a possibility
Mice are an issue for all of us to deal with
I don’t know a lot about pens and deep litter method as I only have ducks and because they were in my house for almost a...
Sorry for your losses
I don’t have a lot of input other then how long has it been since the pen had a proper clean ? Have you thrown away the mouse poo bag of feed so they aren’t eating it ?
I hope you are able to narrow it down so you can save your flock