Sagen 2704N port forwarding issue

[#1]

My assigned port to a device stays open for 1 hour or so and then it cannot be accessed externally and appears closed. 
Anyone else gets this issue? 
The problem fixes itself by restarting the router

[#2]

What Equipment are you trying to open a port for ?
Can you ping the router from the device to keep the device in the arp table ?

[#3]

It is an IP cam so cannot ping anything from that device

[#4]

Not much hope there then
This Thread gives an idea of what may be happening, not sure if plusnet has a ticket open for this problem on not, or even if they care about it.

[#5]

Quote from: 11110_110

Not much hope there then This Thread gives an idea of what may be happening, not sure if plusnet has a ticket open for this problem on not, or even if they care about it.

Yeh sounds like my problem which I dont think wil lbe sorted unless I get my own router.   I spoke to support and it is not something they can help me with apparently, even though I pay for the static IP to be used for something like this.
Joke!  Thanks for your help