If there was a bug in the code where performing a software update adds 23.5 and 19.2 to tuner configuration as well adding a unicable setup, wouldn't other people have reported it too? I dare you to flash a new image, without restoring anything afterwards and setup your tuners from scratch and video yourself doing it. To my mind you are inadvertently changing something and not realising the mistake you are doing. Alternatively, find someone you trust to remote over and assist you.
Yes, a unicable LNB will allow you to get the most out of your receiver. Provided it is configured correcty. The sponsor sells this LNB among others.
https://www.world-of-satellite.co.uk...e-lnb-1-legacy
I think you have a Mk2 Sky dish, so it should have a 40mm collar. If it isn't you will have to get an adapter for your dish or a newer dish.