Hi all

I've been tearing my hair out over this and i've reached the limits of my basic knowledge.

The basic problem is that I'm sharing an FTP service from my NAS out to my parents who live across the other side of the city.

It was working fine for at least a year, but stopped working a couple of months ago.

At the time I looked though the logs but they had been wiped because of an automatic firmware upgrade (Firmware: 06.10-29288 BETA), i did note that the settings failed to restore correctly at the time and then 3 hours later were restored successfully, however the settings were a little bit funny as the wireless was on and I thought i had turned it off and a couple of other things looked out of place.

I've rung Snap and they checked the basic setup and didn't find anything wrong, but obviously couldn't help further with the port forwarding. Which I understand, but i think something's gone wrong somewhere in the firmware upgrade process (either bug in firmware or settings restore).

Here's my current setup.

DYNDNS = uniquename.redirectme.net
Fritzbox (7340) modem (connected to fibre modem), ftp port 21000 forwarding to router on 21000 along with passive ports (55536 - 56559), has DYNDNS configured.
Asus Router, Port forwarding 21000 to NAS: 22000, passive ports (55536 - 56559), handles DHCP etc
QNAP Nas, FTP on port 22000, passive ports (55536 - 56559)

Any machine on the internal network (wired or wireless) can use the external name or external ip and port 21000 and can connect fine.
But my laptop on my cellphones hotspot can't connect, but can connect when on internal wireless.

I think the issue is with the modem, but how do I narrow it down to which device is actually setup wrong?

Any help greatly appreciated!