I was facing the Very same prob with .17 and at times it also crops up in .19

Here is a temporary solution i have found out. Close wazapp and keep the phone in Power Saving Mode for an hour or so (i do so n go to sleep in the night). After that just try n see if it working. Sadly the prob would crop up again in few hrs.

Solution 2 - Reset the setting on ya phone, Worked well for a larger period of time bit the problem returned yest night. But i was able to use wazapp for the whole day without any prob.