NSX native load balancer returns 502 Bad Gateway? Check the header size limits in the HTTP application profile, find the 502 in the Edge LB error and access logs, and verify pool and server-side SSL.
VMs on the same NSX segment talk on one host but not across hosts? Check TEP-to-TEP connectivity and MTU with vmkping, read tunnel BFD state in vmkernel.log and uplink events in vobd.log.
Why a Tier-0 BGP session to the ToR does not come up (VLAN ID or BGP configuration mismatch), how to check it from the NSX Edge CLI, and how to read frr.log and syslog.