Hi
denzellThank you for your asking. Because I have run the same firmware version on my device for 2 weeks yet I haven't encounter the same issue. Please provide the information below so that we can better assist you.
1. Does the issue appear after any system/apps download or upgrade?
2. Please try to enter "Safe Mode". If the function works well in Safe Mode yet the issue remains out of Safe Mode, please check on any disturbance from the installed 3rd party apps.
# How to enter and exit "Safe Mode"
https://www.asus.com/support/FAQ/1005163/3. Could your phone connect to the WiFi on other APs? (ZB602KL: WLAN 802.11 b/g/n 2.4 GHz)