my mx5 was not working 3 month ago after i upgraded to flyme os test version. it stuck at flyme os and keep rebooting with no recovery mode :(
the way i fix this problem. i let the phone drain the battery. and put the place has hot temperature (in dashboard car)in 2 weeks. i lived in Malaysia the temperature should be 32-39 degree celcius. then i let it cooldown and plug in via computer USB(low voltage). then i switch on. i tried this method 5 times. two days ago it boot up and it work. the only problem is the camera. maybe it hardware issue.
hope it fix the problem. :) good luck