Aha! This is why my 2.2.6 to 2.3.1 upgrade would not save my changes!
Bug #6460: Interface Mismatch warning - Apply Changes button is missing
I knew something was off and didn't make sense when all my changes would not 'survive' a reboot.
They were never saved to begin with!
Coincidence maybe, but I remember having other minor issues when exchanging E1000 to vmxnet3 interfaces and had to reassign all of them.
*It could be cool if pfsense could 'auto-assign' the interfaces back alphabetically, by the interface name, etc.
Anyway, good job with 2.3.1p1: Running smoothly (squid, suricata, pfblockerng) with CARP backup, in 2 ESXi 6 servers. (Doing daily backups of squid logs and /root, over NFS to FreeNAS).