4D v19 R3 uses a stronger hashing algorithm for 4D user passwords: Bcrypt.
This new algorithm is automatically used when a password is changed using the Tool Box, the CHANGE PASSWORD command, or the Set user properties command.

Once a password is modified, opening the database with a version prior to 4D v19 R3 will cause an authentication denial for this account.
If you use 4D passwords, it is highly recommended to backup the .4db file (binary databases) or directory.json file (projects) before upgrading to 4D v19 R3 or later.