Port forwarding suddenly seems to have stopped working on Hub One

[#1]

Hi,

For many months I have used a Raspberry Pi on my network (the Hub One is the 3rd router on which I've used this, and all, including Hub One, have worked fine.).  Among other things I use the Pi to back up photos while I am away (I load them to my tablet then SFTP them into the Pi).  So I have port 22 open, and have the router set p with the appropriate applicatios in the Firewall / User defined Games and Applications menu.   Recently I used it every day to send photos back home from New Zealand.  I have a Dynamic DNS set up to track my router.  So it USED to work.

However, in the last couple of days this has stopped working.  If I try to SFTP in, I get this message in the log.

N: ACCEPT [54] Connection opened (Port Forwarding: TCP [192.168.1.117]:22 <-​-​> [51.6.217.21]:22 -​ -​ -​ [51.6.217.21]:1026 CLOSED/CLOSED local_dev NAPT)

I know the DDNS is working fine (I have tried using the IP address, with the same result).  I can access the PI from the LAN, so know it's working.  SO the only thing I can think of is that the router is blocking the traffic.

I spoke to Plusnet help who declare that they don't support this.  I checked my firmware, and I haven't had a firmware update since August, so there's no correlation there.  

I have tried disabling the firewall temporarily, with no effect.

Does anyone have any clues?

[#2]

Has the IP address of your PI changed or did you assign it a static IP?

[#3]

Moderators Note.

Moved to the more appropriate ‘My Router’ board.

[#4]

Yes, the IP address is static.  This is set through the router.

[#5]

I can make it work if instead of using the device name (raspberrypi) I use its fixed IP address.  See attached screenshot.  So somehow the router isn't recognising the device name.  

I can also get Remote desktop working in the same way.

But the router recognises "raspberrypi" when I access it from within the network rather than use the DDNS.  

The log shows the DDNS is updated with the correct WAN IP address.

So I have worked around the problem, but remain puzzled.

[#6]

When I use the device name the log file seems to indicate that the traffic is routed to 192.168.1.117 instead of .87.  Checking the connected devices, the raspberrypi is listed as being on 192.168.1.87.   Could the router be remembering a previous IP address?  Any way of deleting this memory?