Answer
Check that the IFSPRINT password stored in Print Agent's own ifs-printagent-config.xml configuration file actually matches the real, current IFSPRINT database password. If it's out of date (for example after a password change that wasn't also updated in this file), Print Agent's own periodic connection attempts repeatedly fail login with the stale password, and those repeated failures are what trip the account lockout on a short, recurring cycle — independent of whether a report happens to be actively printing at the time.