Help Needed: Tracking Unreachable Traffic and Public IPs in F5 XC

I'm assuming you're talking about an HTTP load balancer based on context here (but feel free to clarify otherwise).

To your first question - look for 503 under Home -> Multi-Cloud App Connect -> {namespace} -> Overview -> Performance -> Http. The requests tab will show (sampled) requests through your LB. You can easily filter for 50x and see under `rsp_code_details` there will be an indication if it's timing out at origin (or no viable origin available, if they're failing health checks). The `dst_site` under a given request will also indicate which RE it was attempting to egress from, so that can help identify if you have consistent RE-specific failures (like a local network firewall block). 

I also* assume you've seen the docs around XC egress IPs per region... but I'm not sure I've seen anything specific to a given RE. Do you have origin-side monitoring where you see connection issues?