504 Gateway Time-out

Hello

I just posted a request for help on How to page, but this is a seperate request for a problem.

I have intermittent issue with 504 messages on the my site which runs on nginx 1.18.0. See attached image.

I can bascially have 4 people access the site and 2 out of 4 will get the 504 and the others will be fine.

Any suggestions would be greatful as still learning nginx and that application I am supporting (open source) and its always a learning experience which is fine, but sometimes along the way its best to just ask for help.

Thanks

Paul