It's been a bug for a very long time. However, with the recent update, it's actually gotten worse and more frequent. Unfortunately the devs haven't acknowledged this bug yet so it's unknown when it will be fixed or even if it's being looked into. It's been reported so many times that either they don't care about it or they don't have the ability to fix it.

But is there any way to get around it? Assigning a different team leader, i suppose, but that's not ideal. Some people don't suffer from it somehow. If i had to guess, i'd say that it has similar origins to how my game settings don't get stored, but i don't know how to fix that either.

Nutaku FKG creates a new dated folder(index_20190227.swf currently) for the settings after every update. I don't think there's anything players can do to keep settings.

The assistant leader is just plain broken. You can see the correct one in the participants list for raid bosses, so it definitely isn't being forgotten.