Changing Mastodon password not possible

It doesn’t seem to be possible to change a Mastodon password of a user created with YunoHost (other users work fine).
And possibly related: Such users also can’t migrate to other accounts - the error message says the password is wrong, though it isn’t.

Hardware: Hetzner Cloud
YunoHost version: 4.3.4.1 (stable)
I have access to my server : through the webadmin
Are you in a special context or did you perform some particular tweaking on your YunoHost instance ? : no