Do Plusnet apply traffic management on certain ports that might cause throttling?

[#1]

I maintain an SSH connection to a couple of servers at home so I can diagnose issues at work.  Since both SSH servers use port 22, I port forward through my router using two separate high ports.  I then tunnel VNC servers through the SSH connection.

I've noticed over the last few days that the connections have been particularly slow.  At first I thought this might be an issue with our network where I work. But I was told that the only throttling we do here is on particularly well-known bit-torrent ports.  So I changed my port forwarding.  Instead of using ports 19036 and 19015, I tried 1036 and 1015.  Problem solved. 

Is this something that PN do?  Are ports above a certain value subject to some form of throttling?  This isn't a moan by the way, just curious.  It would be handy to know so that I know which ports not to use in future.

[#2]

Assuming you're on one of the newer products, there's no throttling on them.

But I was told that the only throttling we do here is on particularly well-known bit-torrent ports.

Not sure if it's still the same, but BitTorrent used to use quite high port numbers.

[#3]

I'm on Unlimited Fibre Extra.  I have no idea if that is a "newer" product or not.  Been with PN since it was F9!