I see users with 1GB hitting the limit from time to time, yet user with 512MB limit hitting it quite a lot of time.
Is it possible that they actually reach the limit. Single PHP process can easily take up 100-200MB, so if multiple processes are spawned it can use that much memory.
Few things you can do:
1. Try setting memory limit to 0 (means no limit)
2. Increasing memory limts, and seeing if they are still hit
3. Check lvetop while running cron jobs (or same command as cronjobs, under user, within lve, via lve_wrapper, or our pam lve module)
4. Using top to check.
Or if you would like -- contact our support or me direct at [email protected]
-- and I would be happy to check you system, and see exactly what is going on.