A hop in the middle failed
502 usually means nginx, a load balancer, or a CDN received your request and then could not talk to the application behind it. The edge is alive; the origin may be crashed, slow, or firewalled.
CDN-specific statuses such as 521–524 describe similar origin problems with more detail. DownSpotter labels those as CDN/proxy errors when we can see the provider.
For visitors versus operators
Visitors: wait, try another region if you have a VPN you already use, and check the company’s official status page if they have one. Operators: inspect origin health, timeouts, TLS between proxy and origin, and recent deploys.