Plex wont load media after installing a new cable modem

Problem: So I started having the infinite loading problem today after a cable modem install and I can't figure out why or how to fix it.

Details: This is a 6+ year old Plex server was running fine up until I changed the cable modem out. Went from a Hitron CODA56 to a NETGEAR CM3000. Both are JUST modems, not modem/router combos. Internet is working fine with the new modem in all aspects except my Plex server is no longer serving media locally or remotely. I can see my libraries, including playback status', but trying to play any media results in an infinite loading screen until it eventually errors out and tells me the media is not available.

So I power cycled the modem, router, and the server, including a full unplug from the wall, and turned them back on in that order. After the Plex Startup Maintenance I got it to play one title but it stopped working shortly after that when I tried to start another title. Again just infinite loading until it errors out. I've found that restarting the PMS exe will grant me that small (1-3 minute) window where it will work as expected including letting me start multiple titles, even remotely, but it always goes back to the infinite loading after that until I fully close it and restart it.

Nothing about the network setup has changed, no settings where changed on the router, no settings on the plex server had been changed until I started troubleshooting. The server is hardwired to the Router. The drives are all showing as healthy and I can manually play the media files without issue. Plex says it's fully accessible to the internet on the dashboard even now as I type this.

Things I've tried so far:

• Power cycling all the devices multiple times.
• Disabling/Closing my VPN. (I use split tunneling and PMS has never gone through it).
• ran 'ipconfig /flushdns' and 'ipconfig /renew'
• ran 'sfc /scannow'
• Deleting everything in the /cache/ and /plug-in Support/Caches/ from the main directory and rebooting.
• Signing out of and signing back into clients
• Verifying router settings (server is using the correct assigned IP, ports are forwarded)
• Disabled ipv6 on the network card just to try even though ipv6 isn't even enabled on my router.
• Verified the network card drivers were up to date and repaired them anyway

Going back to the old modem is an option but I was trying a new one due to unrelated network issues when gaming on a different PC.

I'm out of ideas. I'm confused why swapping a modem would even cause this issue. I'm open to any ideas any of you may have.