Hi
hendradiantoThank you for your asking. Kindly refer to the tips below for troubleshooting.
1. What is your current firmware?
Setting >System>About Phone>Software information>Build Number
Does the issue happen after any system/app update?
2. Please try "Network settings reset"
Settings>System>Reset options>Reset Wi-Fi, mobile & Bluetooth
3. Try to enter "Safe Mode" to test your mobile internet, to check on the disturbance from the installed 3rd party Apps
#How to enter and exit "Safe Mode"
https://www.asus.com/support/FAQ/1005163/4. Check on your "Preferred network type"
Settings>Connecttions>Mobile network
5. Have you tried to open/close Volte?
Setting>Connecttions>Mobile network>Advanced>Disable Enhanced 4G LTE Mode