Problem
Users of the old lichess app are not informed about the new app. The old app becomes buggy and might lead to losing interest into lichess.
Solution
Notify users and advise to download the new app. Probably at some point it makes sense to brick the old app and enforce migration.
NB
I am a huge fan of lichess and didn't know about the new mobile app. It's funny because I follow lichess on various social media, I have even watched the documentary where a lichess developer talks about the excitement about the new mobile app. I'm waiting for the big changes since and the only way I found out was through a bug that occurred to me too: lichess-org/mobile#2557