Tested with 2 other phones. (Guy from the OnePlus forum had 2)
Wiped all 3.
Installed latest beta on all 3
Installed Mycelium on all 3
Worked on one of his, but not the other. Still does not work on mine.
Both of the 2 that did not work are from the original batch.
His 2nd one he got a few months later. So, it's probably a HW issue.
Going to follow up with OnePlus, since on the surface it looks like a HW revision issue, not a Mycelium issue.
-Dave
Hope you are flashing the stock rom not a modified rom. You can download the firmware directly from onePlus, here is the list of stock rom check it here http://downloads.oneplus.net/devices/oneplus-3t/
My guess, maybe your phone is infected with a monkey virus or other viruses like Ghostpush and the Sexy virus that even you do a hard reset or flash it to a new firmware your phone still infected...
You can try to use this tool https://www.4shared.com/rar/FKQZ9lUNce/All_ANDROID_Monkey_Virus_Remov.html
And hope it can delete viruses from your phone. If this tool not work, then you need a box like Chinese miracle or Volcano box to scan the whole system file of your phone and remove all viruses, but only technician have this kind of tool like me.
Anyway, you can try the tool above and the phone must be rooted first to get this tool works.
Since the older stock firmware works but the betas do not, I am guessing it's a OnePlus issue.
That and the ones that don't work are the the 1st shipped 3T units and the one that did was a later shipped one just point to that.
-Dave