I'm not sure...it's still not fixed but better after removing LTE services on my Mi Pad 4 with EU ROM 10.3.1.0.
Some restarts and shutdowns still do not auto-start the Wi-Fi module.
I've scanned through the forum on this problem with Mi Pad 4's and it seems like only the non LTE models are affected.
The China Stable ROM 10.3.1.0 does not have this issue at all, I know becuase I've been using the China Stable ROM for about a month before switching to the EU Stable ROM 10.3.1.0 because of location problems in apps with the China ROM.
According to Mi Pad 4 users the bug still exists in the latest weekly EU ROM, another note is, dirty upgrade from China Stable does not cause the Wi-Fi auto-start bug in the EU Stable ROM.