avigar

Be sure to format the SD card within the camera first. Remove the card and use a USB reader to connect the SD card to the computer. With your computer, download and copy the FWUPxxxx.dat file into the root directory of the card. The camera should find it there during the firmware update.

Version 2.10 firmware is now available for download from the fujifilm site

Please let us know on what needed to repaired on your camera. Thanks!

What are the sizes and age of the SD cards? Have you tried updating the X-T3 to the latest firmware to see if that fixes your problem? I believe the latest firmware is v.210 (FWUP0019.dat) for the X-T3. Copy the firmware, downloaded from the Fujifilm support site, into the old PNY card that works to update the camera. Let us know if that worked for you. Good luck.

I believe the USB-C port only charges the battery in the camera, but not the ones in the vertical grip.

Slot 1, 2, or both? Did anything happen to the camera the last time a card was inserted into the slots? Did you have problems initially ejecting the card from either slot?