This is a new question as of 2020.9.2 but refers to same problem:
The Sim2 connection drops offline (Sim1 is not activated).
Build No.: OPM1.WW_Phone-16.2018.2007.68-20200706.
Thank you for your asking. Kindly provide the information below so that we can better assist you.
1. Does the issue appear after any system/apps' download or update? 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"
2. Which sim carrier are you using? Will the device work with other sim carrier?
3. Try to pull out the sim slot>insert the empty slot back>pull out the slot>put the sim card back to slot and insert back again
4. What's your preferred network settings? (2G/3G or 2G/3G/4G)
5. Please check SMMI test
Calculator> type ".12345+=">SMMI TEST>Single Test>SIM Signal Test/Wi-Fi Test
If any of the SMMI tests fails, indicating high possibility of faulty hardware, kindly bring your device to the nearest ASUS repair center for device checking: https://www.asus.com/support/Service-Center-All-Countries/
If it is impossible to access the service center during Covid-19 period, please try Call us: https://www.asus.com/support/CallUs