I recently got the new cheap JumperTX T8SG (all black) and it was running firmware "deviation-t8sg_v2-v5.0.0-21674bd". One strange problem I noticed was that it would stay in either USB (Enter + Power ON) or DFU (Exit + Power ON) mode. It would get into the mode but not hold it. As soon as I released the power button the unit would turn off. The USB mode was not usable this way since the PC failed to recognize the USB device. Fortunately the DFU mode was being recognized so I use thed Walkera DfuSe tool to load the latest nightly. I had to keep the power button held down all through the update process. It was an anxious minute but it went through fine. With the latest firmware (deviation-t8sg_v2-v5.0.0-48d7be1) the issue is no more reproducible. Just wanted to share my experience in the hope that it may help someone.
Also I am not seeing any of the gimbal related issues with this TX that others had reported.