"An error occurred while processing this directive"

I’ve had this message come up for about 2 months now. I have a VPS server, easily capable of handling my traffic.

I have no idea what the problem is. Every time I get a spike in traffic, I get this message, “An error occurred while processing this directive”.

My host, Hostgator, says…

“It appears that ajax processes are stacking up. These are consuming all the RAM on the server which is causing MySQL to fail.”

I have tried disabling plugins. I’ve tried a Heartbeat Plugin to disable the WordPress Heartbeat. Nothing is working.

Hostgator don’t seem able to help me even though they assure me the server is more than capable of handling my level of traffic (which is true).

Can someone please help with this? Any ideas?

Today’s post on my site, which saw this message appear is here: https://www.musclehack.com/how-this-lady-lost-weight-got-a-six-pack-after-pregnancy/

Many thanks.

Mark