i think bluetooth has been corrected, don't have, till now, disconnection with my smartwatch or with my earphones. But my gps is crap again, i use it yesterday and it jump from street to street like crazy.
umi correct bugs but new ones appear.
My understanding is that once you install a custom recovery or even root your phone (depending on the method), you've alterered the internal structure of system files. And so FOTA might not work properly anymore. The way to solve this properly is to flash again the stock rom using the tools and instructions provided in the support section and then FOTA will work again: http://www.umidigi.com/page-service.html