For some unknown reason, Chinese smartphone manufacturer always include aggressive app killing in their system. Huawei/Oppo/Vivo/OnePlus/Xiaomi all have aggressive "battery optimization" that will kill app literally every time you sleep/wake your phone and they only bothered to white list popular app like WhatsApp/Facebook. You probably need to manually white list Ookyo app so that it wouldn't be auto killed.

There is a speed cap for streaming and streaming anything above 480p will result into multiple buffering while watching video however it's still utilizing the unlimited data.