I've had this problem as well.
I have the USB C connected to the front of a brand new Xbee TH,
a microUSB connected to the "USB Direct Connect" through a USB Hub.
The first time, after updating to 11415 (from 11413) the "updating radio firmware" pop up "Details" text box said
- Waiting for module to reset... [OK]
- Transferring cellular modem firmware...
It got up to "Programming cellular modem : 98 % and failed with the following
u-blox AG EasyFlash CLI downloader v.10.02
Please TURN ON the device and don't disconnect power supply
Waiting for device...
Mobile Version report: PASS
Ext Mobile Mobile SW Rev: L0.0.00.00.05.06
-> Backup of legacy NV objects
Process time was 14.4 sec.
-> Backup of ublox legacy NV objects
Process time was 31 msec.
-> Backup of RF NV objects
Process time was 4.5 sec.
-> Backup of CONF NV objects
Process time was 3.1 sec.
-> Switching to emergency download mode
Waiting for synchronization...
- Transferring cellular modem firmware... (retry #2)
I tried a 2nd time powering off the XBEE/XB-TH board, waiting 10seconds, then powering and trying again.