NGINX | 从上游读取响应头时，recv（）失败（104：由对等方重置连接）

Question

I have been getting this error message and have tried almost everything i found on internet that says to fix this issue, but I've had no sucess :(

recv() failed (104: Connection reset by peer) while reading response header from upstream

I am using WordPress on a VPS, with 8-10 domains on the same WordPress install. For all the other sites I've seen no problem but for the master site of WordPress install whenever i goto any page, I get 502 Bad Gateway

None of my pages are working. From what i can see whenever any page on site is opened then PHP-FPM crashes with below error:

child 991195 exited on signal 11 (SIGSEGV) after 18.490300 seconds from start

and this thing keep on happening every time page is opened on this site.

Please help me with a full proof way of identifying the root cause with this issue and on how to fix this.

Many Thanks for your help.