@julian Upgrading to 2.5.2 totally fixed the issue.
Many thanks !

@julian I will ! (and keep you informed).

Thanks for pointing me out this fix.

NodeBB version : 2.5.1 (installed on Linux Ubuntu host)

Our server was running for several years, and we decided lately to upgrade it to 2.5.1
Upgrade procedure was successful, and all features seems to work, except that new users can't create new accounts in the forum.

The issue is that when the try to enter a password, there is an error under the password field saying "t is not a function". Thus, the "Register" button (in french in the screenshot below) is disabled.

The issue is reproducible on many browsers and OS.