Didn’t expect the Windows hotspot feature to make a difference tbh. Good to know (although I should be fine anyways since I have unlimited data on O2 and temporarily unlimited data on Vodafone too).
For Apple devices they do need to be cellular for a hotspot to work but a lot of Android devices are able to hotspot from WiFi too.
Your post sounds very confusing, you can create a PNID and do a some stuff on Pretendo using the SSSL method.
Sky won’t be blocking Pretendo. Not sure if they hold a list of blocked domains, but Virgin Media do and pretty much all the domains blocked host illegal content.
Considering it works for you some of the time, it’s probably just most likely something with Sky still.