Missed schedule – busy site – working cron

Hello,

I don’t want to install any additional plugins. I’m trying to find out why this issue occurs.

The site consistently has over 500 users active on the site.

Normal cron is disabled, and is run as a server cron job every minute.

Heres the thing – scheduled posts sometimes work (50% of the time) and the rest of the time, they missed their schedule and i see a ‘missed schedule’ notice.

I’m trying to work out – how is this possible?

Thanks