My website crashing every hour now. Hosted on AWS.

I am using WPLMS and have got some custom plugins created for my wordpress website by a developer who has recently left my team. Everything was working fine but now, we are facing some critical issues. The website is crashing every hour now, it started almost daily a few days back. There are some errors which I am listing here for understanding the issue:

http://prntscr.com/bffqvu
AWS EC2 Status screenshot

http://prntscr.com/bffr69
AWS RDS Status Screenshot

http://prntscr.com/bfg84v
website errors page - console display

When I restart my EC2 instance, the site starts functioning but within hours it goes off. Then I get this error.

http://prntscr.com/beksxt

Appreciate your help to restore my wordpress site.

Thank you so much!
Aryan