I have moved to ports 4990 - 4995, also, I have forwarded these ports in my router as well. I don't know why the game is asking me to forward ports I do not use, but it is causing a lot of connection issues.
did you tried to disable "Enable UPnP" and "Enable NAT-PMP"?
These two Services tries to tell your Router Ports to Forward to your Machine.
If you manually set your Router to forward these ports to your local Machine IP you have no need to use these.
And maybe if these services are active Warframe tries to use the default Ports.
Did you test the forwareded ports with maybe check-host.net/check-udp