You might also want to make sure your external IP address hasn’t changed.
If you have/had a static IP and you changed your modem at the same time as your router (or they were the same device) your static IP might have been changed underneath you.
If you have a dynamic IP make sure you have set up dynamic DNS again with your new router.
Hello. Yes, I checked on that and it had changed. I maintain my subdomains and made sure they were pointed at the corect physical location IP.
I had an epiphany, this morning- "What if the router wouldn't work work with port forwarding with the main IP changed?" So, I rebuilt the network with the default. I'll have to rebuild the NextCloudPi instance and run a new letsencrypt cert because the software on it is locked to the older static IP. I've tried to get in to clear it, but I can't seem to. Not a big deal since I want to change a couple of settings and build setups, already.