Here the situation is totally different.
I have owned 2 Mi A3 phones.
Both were upgraded to A10 (Evolution X with root). While one was stable, the other suffered from automatic reboots when the screen is locked (usually when I'm asleep) or while unlocking the screen.
Both were originally European versions of the phone, but the custom A10 ROM may have installed a global firmware/vendor.
The stable one I gave to my sister and she's still using and upgrading it without problems.
I kept the unstable one for myself and I've tried to repair or at least find out why it reboots by installing different ROMs (crDroid and Evolution X) and different kernels (Bit and Fenix) but so far I've not been able to solve the issue. I've looked at the logcat and even send the logcat to the developer of some custom ROMs.
I suspect that the reboot happened because of the phone activating itself to look for new messages in the background (while the screen is locked). Maybe the phone was switching between different sleep/active states. The reason I suspect this is because I've seen at least once that the reboot happened around the same time that I see in the logfile of my WiFi access point that this phone is having some internet traffic.
Sadly I don't have the right skills to develop my own custom ROM, but if someone with these skills is reading: If you have time, please make a custom ROM based on A9 with signature spoofing and root. I was still using Kitkat a half year ago, so I'm not in a hurry to use A10 or 11.
Update:
I've just read some one suspect that the reboot is caused by the phone trying to adjust the brightness because he was walking out of a building when the reboot happened... so maybe in my case it was the phone (while the screen is off and locked) is receiving a new message and trying to turn on the screen to show the notification.
Well thats definitely big concerns.. however.. a10 is just out for this device in may update! So waiting for more fixes !
I think dev. Should concern about the feedbacks and bugs..
Not worth to use like this..
I am not ROM developer i have seen only miui11 Working for a9 but i dont like miui at all..
I dont think anyone will make rom for a9. Coz its very irritating work to rollback !
I only like stock rom!
Am just waiting for PIXEL EXPERIENCE..
The rom u use Evolution X has not good camera. Like stock..
I want 99%✓✓ ok custom like stock..