Hi inghgreenc,
We would suggest you update to the latest firmware version WW-16.0610.1905.79
and check again.
You may check update in Settings > System > System updates, or download from our website: https://www.asus.com/Phone/ZenFone-5-Lite-ZC600KL/HelpDesk_Download/
How to manually update: https://www.asus.com/support/FAQ/1009748/
If the problem still appears in WW-16.0610.1905.79, please provide us the information below:
1) Please try resetting your network. (Settings > Connections > More > Network settings reset.)
2) Please tell me your mobile network provider
3) Please show me a screenshot of the signal strength when the problem appears.
(Settings > System > About phone > Status > SIM status)
4) Please change to another SIM card by another network provider, and check if the problem still appears.
Please also put your SIM card into other phones and check if the problem appears.
5) What kind of location does this happen? Are you in any building/ on a transportation/ in the basement/indoors or outdoors?
Thank you for your help :)
Please check in other locations as well.