Hello,
I have a strange problem since the version 7.6.5. It also happens with 7.6.6 and 7.7.x. Once per 50 or 100 pageloads, I have a 502 (bad gateway) or 405 (not allowed) error. It can happen with all type of mouse click (save, edit, refresh, …).
I have another Wordpress installation on the same shared hosting and no problem there.
Do you have an idea of what it could be ? I already tried a lot of things found on internet but nothing works … Any tip would be very kind 
are you using a webserver?
Yes, a shared one …
try checking your webserver,
error 405 as you said it won’t allow the method sent. the possible cause for this one is that the length of the characters that your method has exceeds the limits of 127 characters of the load balancer. for this error, you need to go back and check the length of the method if it exceeds try modifying it to meet the 127 characters limit.
as for the error 502. i still didn’t encountered it but you’re right it is a bad gateway error. might as well check the gateway of your web server.
good luck!
Ok, I tried with another provider, and no problem anymore … Strange … Thanks !