Hi, I have applied below steps and got fixed the issue on my K20 Pro:
1. Format data by TWRP
2. Download and flash the stable 10.3.15.
3. Launch and setting your MIUI 10.3.15 (like add google account, install some apps)
4. Then continue downloading and flash the stable 10.3.16
After successfully flash 10.3.16, you launch and use the phone as normal and the issue should be fixed.
Please try doing the steps and let me know the result.
Thanks.