Missed schedule

I have been using WP for now 8+ years and never got this problem. But since last week all my scheduled posts “MISS” the scheduled time and I Have currently 60 posts Scheduled.

Of late I have been using my iPad to update and work in WP in admin mode. And I also have upgraded the WP version from iPadbrowser. Do you think that could be a problem? Or is this some issue with the latest version of WP?

Please help and guide to solve the problem. I am a bit hesitant in using any plugin which executes every 5 minutes….

Thanks in advance.