I think you need to find out what is going on in cron. As Emma suggested, there are real problems that occur in there. And running out of memory during cron, really points to a problem in Moodle I suspect.
I wonder what logs you looked at. The apache php error log and access logs won't contain errors that occur in cron. Because they run outside the web environment usually.
A simple thing to do is to go to site admin -> server -> tasks and look at the task logs. probably for failed tasks.
A classic issue can be if adhoc tasks are queued up to the sky. I have seen sites with 40,000 tasks waiting to run. This can happen if long running tasks dont finish in the cron window and everything else queues up. I am not sure of the best way for a site admin to check the adhoc task queue. Perhaps there is a report somewhere for that.
On dev sites I often have cron turned off and run it via my browser and watch the output.
I wonder what logs you looked at. The apache php error log and access logs won't contain errors that occur in cron. Because they run outside the web environment usually.
A simple thing to do is to go to site admin -> server -> tasks and look at the task logs. probably for failed tasks.
A classic issue can be if adhoc tasks are queued up to the sky. I have seen sites with 40,000 tasks waiting to run. This can happen if long running tasks dont finish in the cron window and everything else queues up. I am not sure of the best way for a site admin to check the adhoc task queue. Perhaps there is a report somewhere for that.
On dev sites I often have cron turned off and run it via my browser and watch the output.