I also ran into this problem. I noticed that I didn't have a `/sbin/upgradepkg` any more but I did have `/sbin/upgradepkg-`
❯ ls -l /sbin/upgradepkg*
.rwxr-xr-x 16k root 5 Dec 2024 /sbin/upgradepkg-*
Rebooting did resolve it for me. If it's helpful, I had been updating things. I first installed the official patch installer and then I did update all plugins.
I wasn't able to figure out how to do it from the command line but you can trigger unraid to refresh the DHCP lease by going to network settings and then changing a setting and then just changing it back and then, finally, hitting apply. The big downside to that is you have to stop(or disable?) docker and VMs in order to have it let you do it.