tex87, Jan 10, 2019 : Hi there! I've got my new OP6T almost two months ago but I faced the issue almost instantly. I waited for some Oxygen OS and apps updates but the situation is the same as two months ago. I read an article saying that OnePlus is at the second place of the companies with the most background app killer software and it's true (IMHO)! I experiences this issue with Whatsapp. Pratically after a couple of minutes after I turned off the display (with Whatsapp still running) the phone seems to reduce the responsiveness of the app. I see many times a "checking for new messages" notification. Even if I connected with Whatsapp web, after a couple of minutes (like 15/20), the browser page tells me to check if the phone is still connected. If I reopen Whatsapp everything working normally. Someone else is facing this issue? Thank you.