Random 502 bad gateway

I have come across a stange issue recently. Randomly 502 error appears on website.

But when the webpage is refreshed, the 502 clears & page loads fine.

I noticed this issue during following times (randomly);

1) When trying to login via backend (couple of times)
2) When trying to update pages (came across this issue once so far )

3) I have few pdf eflyers (emailed to customers) with a link to specific pages on website. Sometimes when a link is clicked on pdf eflyer, 502 error comes.( When refreshed, page loads without 502 error )

Website is on inmotionhosting (cpanel account).

Any specific thing to look prior to checking this issue with hosting provider? Is it some issue on wordpress or plugins ?

Any help is highly appreciated.
Thank you.

 

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