5ghz speed dropping daily.

[#1]

I went to the Ombudsman.
They are impartial (but part funded by Plusnet).
They sided with Plusnet.
You need to raise a formal complaint ticket with Plusnet & wait 2 months without resolution to go to the Ombudsman.
Beware, Plusnet automatically close your ticket if they (or you) don't update it for 1 month.

[#2]

I should add, I did get a small payment from the Ombudsman for the failings in Plusnet customer service's handling of my formal complaint.
It was not in any way for the issues caused by the firmware update. The ombudsman repeated Plusnet's stance that they are not responsible for WiFi due to the many factors which can affect it.
Even though we all know this was a Plusnet firmware update.

[#3]

I am getting texts telling me to close this issue if its ok now.

ITS NOT OK. DO NOT CLOSE MY CASE UNTIL MY 5GHZ IS STABLE AGAIN