What service do you have and what hardware? With v2.50 came a lot of changes as well as FreeBSD v12.2. New NIC drivers were added, others updated and some dropped. I’ve seen this error before but it’s been quite a while.
Assuming you’ve rebooted your ONT/modem and pfSense, have you checked to ensure the WAN interface is set as the default gateway/route? If you’re using a VPN client make sure it didn’t get switched to that interface. What does your routing table show? You might have to force the speed/duplex on the WAN interface to match the modem (instead of auto select). I’ve had to do this on a pfSense box and ATT issued Arris BGW210 modem before where pfSense would fail to negotiate/renew the WAN IP when the lease expired. Shortening the lease time also seemed to help. Some people have even put a dumb switch between their modem and pfSense to help the devices negotiate. Disabling TSO and LRO (System > Advanced > Networking) might be worth a try.
I’ve been running pfSense v2.50 at 3 locations with varying hardware since last week. Outside of some cert related bugs and NCP getting broken with some VPN providers it has been pretty solid.
If all else fails and v2.45 worked fine then you could always downgrade if you kept a backup. Or, you can do a clean install of v2.50 and see if that resolves the issue.