Forwarded Ports Keep Closing

I have a VM Superhub set to modem mode, and my RAX200 connects to that. The system works fine.

I have a wired streaming camera (fixed IP)  which requires ports 554 and 80 to be open for the RTSP stream to be read. I have two rules which open those ports, and Open Port Checker confirms they are open. Everything is fine at that point.

But for some reason, periodically the camera stream goes offline and I find that ports 554 and 80 are now closed. I have to reboot the RAX200, and then they are open again and everything is working once more.

UPnP is disabled.

Since rebooting the RAX200 resolves the issue - albeit temporarily - I am assuming the problem lies there

One additional (but unconfirmed, because I will need to check this) detail is that if I delete the rules and create two new ones, that also opens the ports. I think I did that the first time a couple of weeks ago until I discovered rebooting fixed it, but I will check next time.

Does anyone have any ideas or suggestions?

Thanks