Excuse me but you're wrong. I have very strong 4G signal, but my phone switches to weak 3G signal. Once after a reboot i had stable, strong 4G signal for like half an hor but after that it dropped to 3g again with almost no signal at all.
I can confirm that on my Z Pro I will experience signal loss and frequent switching of network speeds while my wife (who uses a Sony handset) who is on the exact same mobile network provider as me experiences no issue at all.
I personally believe that "SOLVED" should be removed from the subject line of this thread.
Same here, my UMI Z Pro is switching from good 4G Siganl to 3G with bad signal... Only Reboot or Flightmodus do a switchback to 4G for max 20 minutes...