I think the home button just failed coincidently. The update could'nt have caused the home button to fail. You tried to hard reset the phone yet?

Then only choice would be is to send it back for RMA.

Come back home only rma. No choice but to get another phone first.

what firmware are you using ?? if you using  latest firmware lollipop , meizu changing something for home button function you need to format and clear data.

then do replacement for screen berapa?

Yeah haha. I don't see any MX4 Pro clearance? 
Although you are a certified phone technician, I think at this price it's not worth to fix it already haha.
Yes it is. For the price, it's much better than Xiaomi build quality to be honest.

I remember the LCD was quite good and sharp. The ratio was odd though. The strongest impression was the built in speaker. Although single firing, it was blardy loud and clear.

And of course I hate the lack of back button and multitasking. Apparently Meizu thinks it's faster to use gestures vs buttons. All that just to retain the one home button look as iPhone.