Port Forwarding - Open then Closed

I've been trying to port forward a device on my network and open port 44158.

Logging into the Virgin Hub 4 was pretty straightforward:

1. Located the device on my network that I want to open ports for
2. Created a Reserved address for that address (static IP)
3. Created a port forwarding rule for 44158 (TCP/UDP)
4. Restarted router and all works fine.

EXCEPT: the port appears to be opening and closing randomly. When I use any port checker tool (like portchecker.io), the status of that port for my IP address will show open for several refreshes and then closed for several and so on.

Things I've tried:
-I've tried this setup with uPNP enabled and disabled - no luck.
-I've tried putting the Hub 4 into modem mode and using my Netgear Nighthawk R7000 as the router, opening ports etc - no luck (this rules out a problem with the Hub 4)
-I've pinged the device and now and again I see some packet loss, but only about 2 lost for every 100 pings
-I've tries to create port triggers for that port - no luck.
-I've created DMZ entry for that device IP - no luck.

This is a bit higher grade for me, so any ideas what could be happening here?

There's a few things worth pointing out here

Have you confirmed the port opening/closing is an issue at the application level of whatever you're forwarding to, as opposed to being an issue at the router?

44158 is an unusual port to be forwarding and is arguably part of the ephimeral range - why this port and can you try moving it to a lower port number. This may resolve the issue.

I'd keep UPnP disabled and then restart the router to clear out any transient port forwards created due to UPnP.

Finally, perhaps there's a firewall on the virgin hub or your PC/server/application which is blocking this due to a port scan type detection. I don't know anything about the virgin hub though so that's just speculation. If the virgin hub has some sort of magic firewall settings try reducing or temporarily disabling and see if that helpos.

OP must've cross posted it......thread discussion has more detail here:

https://forums.thinkbroadband.com/virgin_cable/f/469...