Nginx Weird connection error randomly

I've been getting complaints about this connection error randomly. It's on different sites, all the sites are behind Cloudflare. I run pings on the machine and they aren't losing connectivity. I don't see anything in the logs. I'm not even sure what error message they are getting.

Cloudflare handles the DNS as well. These are all centminmod servers, different servers behind different hosting providers, different domains.

About the only thing that's the same is they are all running the latest version of Centminmod, although on various OS versions, all Alma 8, 9 or 10...

---

Sometimes just doing a page refresh and it works. It's got me tearing my hair out, and it's from multiple users, locations, etc.

Any idea what it could be? Please see attachment:

 

Awesome, thank you!

 

This is disappointing. I don't want to have to disable HTTP3/QUIC to fix this.... Xenforo needs to do something about it.