Hi Karim,
I tried to reproduce your issue unsuccessfully (the register on the project table is deleted without a problem), do you have any element/config of that project to reproduce it? (some SCM config, schedule jobs, a specific plugin, node executor, project config, etc…).
Now, please test this in a non-prod environment first:
Change the project state value to ENABLED and try to delete it again. This field is a safe flag to delete projects (Rundeck disables the project first and then tries to delete it). I presume that some action keeps that field in the ‘DISABLED’ state (for example, a large number of executions causing a session timeout; if so, enable it and erase all executions before attempting to delete the project).
Greetings.