Which NSX-T and Log Insight version are you using?
Did you check if the VMs have VMTools installed and running?
I tested in a lab with NSX-T VLAN backed segments and it is working fine at my side, i used the query vmw_nsxt_firewall_src starts with <your IP>. For some reason contains does not work for me to get the results.
You can also query on appname contains firewall_pktlog.