I have the same issue on my BV8000 Pro, after last update VO.1_20170803_20180105-1104
I get no notifications from WeChat/Whatapp unless I unlock phone and start the app? This was not a problem before. Being told to do a factory reset does not sound like normal Android procedure on any other phone, and its the first time I hear of it. I will try the "Background task clear" suggestion and hope it works. But this sound like a definite update issue...
Yeah, this bug has been reported. We are waiting for the tech team to fix it.
In this case, performing a factory reset will not solve the issue (as confirmed from different users).
The workaround should do the job, al least for the moment.