Port forwarding, works fine for a bit, then stops :-(

[#1]

Hello, just switched from ADSL to fibre and setup port forwarding as before for my IPCAMS (which I rely on).
All works fine for a bit and then stops working....
1. First router supplied, stopped working after 10 mins.
2. Second router supplied now last for a few hours.
Have gone into routers expert_user settings and disabled ipv6 dhcp. Just trying to eliminate what the issue could be.
Appreciate any advise or assistance - thanks!

[#2]

I don't think you're alone, I've seen other threads round these parts describing a similar problem:
https://community.plus.net/forum/index.php/topic,140665.0.html
https://community.plus.net/forum/index.php/topic,139281.0.html
http://community.plus.net/forum/index.php?topic=139407.0
http://community.plus.net/forum/?topic=140012.msg1234844
Have a look at the screengrab attached to this post. There's a page at 192.168.1.254/expert_user.html that grants access to these settings. It might be worth you adding the MAC address and IP of your cams to the Static IP Lease List and see if that helps (although the poster in that thread had limited success it would seem).
Alternatively, you could try playing with the port triggering settings.
I'm sure I've seen somewhere, that assigning your port forwarded devices an IP outside of the DHCP pool can help too, although I'm struggling to find any discussion about that after a quick search.
It's funny because I was using this router for a month or two before we started shipping them and port forwarding for the 5-6 servers I have running at home presented me with no problems whatsoever (the servers were all outside the DHCP pool which I changed to 192.168.1.101-192.168.1.253).
It seems something's definitely amiss though, and it would be nice to establish a guaranteed fix/workaround. We also need to find out what's causing it. This is an interesting assumption from Darsh, although it wouldn't explain what this customer has observed.