Lemmy Devs are aware there is an issue with 2FA and are working on it.
https://github.com/LemmyNet/lemmy/issues/3309
For now, until its fixed, we would recommend you don't use 2FA.
We have now upgraded to Lemmy 19.3 and there should no longer be any issues with 2FA
We have now upgraded to Lemmy 19.3 and there should no longer be any issues with 2FA