There are a few things why this would occur:
There is no authorisation rule, ensure you have a rule set up.
Check who added the Logbook.
📌Note: If you have a rule set up for added by the manager and additional manager if a manager's manager adds the Logbook this will not go for approval as they are not the employee's direct or additional manager.
If it is a manager's manager who is adding the Logbooks, we advise editing their access rights to this Logbook and then creating an authorisation rule for submitted users with edited access rights to ensure the request goes for approval.