Do you mean "Static Mappings"? I have a couple dozen of those and had no issue during my pfSense upgrade. I also rely heavily on two settings in "Services > DHCP Server":

- [x] Enable DNS Registration (leases will auto-register with the DNS Resolver)

- [x] Enable Early DNS Registration (static mappings will auto-register with the DNS Resolver)

I do not use the "Create a static ARP table entry for this MAC & IP Address pair." option for individual static mappings.

Hopefully this helps you in your troubleshooting.