I've the same issue after recent OS update and contacted tesla for the fix.
Fix For OnePlus:
System Settings -> Battery -> Menu -> Aggressive Doze & App Hibernation(Turn these off completely)
Also under that menu High Power Usage Apps, if Nova Launcher/TeslaUnread show here, disabled them
System Settings -> Advanced -> Recent App Management -> Normal Clear should be set, not Deep Clear
Apps -> Settings -> Apps Auto Launch(Turn this on in the top right corner and turn it on for Nova Launcher and TeslaUnread)
Once you have that set, it should work properly and stop turning itself off. However, if you're not using one of the above branded devices, then it's probably something very similar that you need to do. If you can't find anything similar then you will need to contact the manufacturer of your device.
But the above didn't worked for me. But reinstalling did the trick. Thanks!