When configuring a new user diretory with an existing table (not created by Ametys) the table is dropped at the next reboot because we execute the initialization migration for user-directory.jdbc.

When creating the directory we check the existence of the table. If the table doesn't exist, we run the initialization migration to initialize the table.
But if the table is present, we do nothing, so the initialization is run at the next boot because the version is computed based on defined population but the version is not initialized.