For my original problem, I think I found a bug.
For some reason the user password length was set to 0 (I didn't set it that way, it's not possible). When I set up my forum, my password was 7 characters long (before launching the site, I change the password to a complex and unique one, but during the development process I use a simple one that I remember). When I transferred the forum to the server and edited Users -> Settings, I set the minimum password to 8 characters, because it was impossible to leave the field with a default value of 0. And here I see a bug, because no one expects this behavior. Once the minimum password is set, NodeBB simply stops accepting any passwords that are shorter. This is completely non-obvious and as an admin I fell into a trap. I would expect two behaviors:
Снимок экрана 2023-02-01 в 14.04.48.png
