Spark should be supporting only those devices that are official chrome casts or officially running android OS/TV.. the list for chromecasts is quite small and the official phones are easy as they have google apps installed at the get go. outside of that, all those custom chinese boxes are the edge cases.
I've been testing the chromecast to shield from my laptop to the shield in the lounge and so far I haven't had any issues with the qualifying reply, so I reckon its either the phone or the app in conjunction with the phone, espeically since Talkiet has no problems with his Sheild.
Was also talking with SS support and they now expect paid subs even though the service is still classed as beta. I get today's race as part of the 1st month trial but after this ends I'm not confident I will resub, $20 a month for a single sport on a platform still in beta and with issues I'm not sure that is value for money there... When the EPL starts then it would have more value as I currently pay sky $16 a month for that access through bein so will have more value but right now, its a tough ask.