SFTP and FTP keeps dropping / locking up

Hi,

I purchased the Nighthawk X6 R8000 a few weeks back and generally its been good. With the exception of 1 thing - it keeps dropping my SFTP connections! I'm using WinSCP, and I've never had this problem before with my old ASUS router. Is there something I need to do? I'm using non-standard 22122 port numbers, so maybe I need to configure something around that? (obviously port 22 is the standard port).

When the issue occurs, I am trying to download/upload a file, and after it hangs for a bit, I get a WinSCP error telling me the connection has been lost. It then reconnects, and does what its supposed to. But this obivously isn't good and not something I'm willing to  put up with.

FWIW I'm on a wired cable - not WiFi

Thanks in advance.

Andy