I'm in the same boat.
G10T and Yamaha THR30II purchased Late November 2019 and have operated flawlessly until I followed the instructions to upgrade the firmware.
I updated the firmware to G10T Version: 1.06, Amp Version: 1.42.0g
When the G10 is inserted into the THR I see the slow flashing red light, indicating charging. However, it will not charge up. I get maybe 10 mins of use before it dies completely.
Prior to the firmware update, the G10 would flash bright red initially, then change to flashing green and eventually solid green. I would routinely get 4-6 hours of use between charges.
The response from line6 is that this could be a hardware issue and to return the G10 to the retailer. Not very helpful since the G10 is out of the 12 month warranty period.
I don't believe this is a hardware issue. The G10 was functioning perfectly prior to the firmware update and stopped charging immediately after the update to Firmware 1.06.