Port Forwarding Hell: TCP Rules Work, UDP Rules Don't

Hi there, I've got a Dream Machine and I've had intermittent issues with port forwarding for awhile. While I know UPnP is an option that could solve this, I'd rather figure out what is going on here.

While I'm far from a network technician, I am generally tech savvy and at worst, can usually Google my way to a solution. This situation I can't make heads or tails of.

None of my portforwarding rules that are UDP only or TCP/UDP work correctly for UDP traffic. TCP rules and TCP Traffic on the TCP/UDP ports work just fine.

This issue is most glaring on my homelab server where several file sharing protocols are at least partially broken. On torrents, I don't connect to nearly as many peers as I should. On DC++ (which uses UDP on port 21248 exclusively for search) I get zero search results.

I also am unable to connect to Xbox Live at all even with all ports forwarded correctly. When I take the same Xbox to another house, it connects just fine.

The DC++ issue was the first thing that alerted me to the fact that I specifically have a UDP issue, because everything BUT search works fine and the only thing UDP is used for with DC++ is search.

I've used https://check-host.net/ to check my ports. All the TCP requests go through normally, but all the UDP requests say "Connection Refused"

Any idea what could be happening here?