If it's going to keep happening, perhaps export / import options would be a good idea?

Are you using other clients? They are probably erasing your lists when you follow/unfollow people. If exported and imported then it would erase the follow/unfollow you just did.

I do not use any other clients.

I didn't follow or unfollow anyone recently either.

Very strange. I will see if I can find the bug somewhere.

Sometimes the list returns and sometimes I have a different list because I started a new one after losing the first list. Also sometimes I have a list that looks like a combination of both lists merged. Are the lists stored locally or on a relay server? If a relay is down at times would this cause a list to disappear, and then I started a list stored on another relay, and when both relays are active I get the merged list? Just brainstorming because I'm not sure how they are stored.

This is happening to me too. I lose filtered words and also the block list goes empty. I found if I keep closing and reopening the app that sometimes after a bunch of tries it will come back.