Suite CRM cron stuck in "running"

I keep getting CRM inbound mail getting stuck.

I have to remove the scheduler ID from the db like this:

select id,name from schedulers;
delete from job_queue where scheduler_id = ‘5e5b3089-6f2f-813c-9f0e-53fdc5c23424’;
update schedulers set last_run = subdate(now(),360) where id = ‘5e5b3089-6f2f-813c-9f0e-53fdc5c23424’;
commit;

This ID belongs to “Check Inbound Mailboxes” which is stuck in running.
The mail server is dovecot on the same machine (Linux) running PHP 5.2.8 and Apache 2.2.3.

Once I delete this, CRM runs fine for days but then gets stuck again.

What is being polled? Is the mailserver large?

Do you get any errors in the job_queue table description for the scheduled job, or in the sugarcrm.log or apache error.log files?

Thanks,

Will.