
Explanation

Backend instance health: Health Probe Status
Health Probe Status (DIP Availability): Standard Load Balancer uses a distributed health-probing service that monitors your application endpoint's health according to your configuration settings. This metric provides an aggregate or per-endpoint filtered view of each instance endpoint in the load balancer pool. You can see how Load Balancer views the health of your application, as indicated by your health probe configuration.
Outbound port exhaustion: SNAT connection Count
SNAT connections: Standard Load Balancer reports the number of outbound flows that are masqueraded to the Public IP address front end. Source network address translation (SNAT) ports are an exhaustible resource.
This metric can give an indication of how heavily your application is relying on SNAT for outbound originated flows. Counters for successful and failed outbound SNAT flows are reported and can be used to troubleshoot and understand the health of your outbound flows.
Reference:
https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-standard-diagnostics