Similar issue here under ESXi 7.0 and pfSense 2.4.5-RELEASE-p1.
Created a VM with one virtual NIC, booted installed OK.
Powered off, added 2 other NICs, booted and they are OK.
Added a 4th NIC while powered on, the VGA console shows that at operating system level it was detected hotplugged with correct MAC address, but in pfSense web interface did not appear.
Rebooted, still not there.
Powered off and back on, still not there.
Deleted the whole VM, re-created from scratch with 4 NICs, re-installed pfSense from ISO, all NICs present.