Using the 3rd child's PC with IE gave a perfect viewing experience for PLP. I have since restaged my 1st child's laptop and that works fine too now.
My own PC is a beastly fella and gives a perfect experience no matter what is running on it. I can only watch PLP in my office on a 27" monitor as its not a portable thing.
Also, even though I have a good wireless network I choose not to use it for PLP. My experience is that this introduces delay during live streams. So all my usage in the house has been via a wired connection. This for me seems to give a better experience.
That said last week I had a perfectly good time watching a mid week game on my kids Samsung over an LTE connection.
Seems to me that the hardware matters. I'm wondering if those that are having bad times are using wireless or poor PCs perhaps.