502 error only on cloudflare suddenly (pausing cloudflare fixed it), no setting changed

Hello there,

Give it a try

Check your Origin server for configuration
Check your DNS TTL value if you have set to Auto (recommended) or certain value
Check your server log for various reasons:
It could be due to overload, crash, traffic spike. So, it can be temporary basis on your server
If you are specifically trying from one device, clear the cache and flush DNS from system

For more guide: