I am getting the same sort of thing
I have SkyGo extra and watch it through my PS4 and it can be fine one day and then go to watch again and it says I've reached the device limit. Sometimes it also removes itself completely from my list of devices but not all the time, either way I get the same error message.
Have phoned sky 4 times to have it sorted, it works for a while and then happens again
Will be phoning them again tomorrow and demanding a more thorough investigation as to why it keeps happening