DNS loses record anfter a while when using "Register DHCP leases"

[espenu]

We are having some issues with DNS records getting lost when using DHCP and "Register DHCP leases".
The problem is that if the clients have been off for a while, the lease expires and the DNS record is gone (as expected). When those PC's are then started again, they get a new DHCP lease, but no DNS record. Restarting the DNS service makes them all appear again.

We were first using Unbound DNS, and then tried switching to Dnsmasq in case the issue was in Unbound.
Both Unbound and Dnsmasq are set up with both "Register DHCP leases" and "Register DHCP static mappings".

If all PC's are set to use static DHCP lease this problem goes away, so we can work around it, but we would prefer to be using dynamic lease.

At the moment 24.1.2 is in use, but we have seen this problem since the system was set up in September.

Our system has multiple opnsense routers which all have this issue, and none of them are internet facing. They all use another opnsense edge router for internet access.

Any idea what could be causing this?