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.
Host Down or Host Disconnected in NSX? Which NSX host agent is behind it (nsx-proxy, nsx-opsagent, nsx-cfgagent, nsx-nestdb), how to check and restart it on ESX, and which logs to read.