Hi Laurent,
I'm at the moment not sure what is happening in this case.
I think there might be some issues be related. The XL6009 getting crazy in combination with low input voltage or the TP5100.
I will have to check this on an oscilloscope.
On top the protection board - there might be some current peaks / or maybe backward voltage in combination with the XL6009 without load - bringing the protection circuit to switch off immediately.
For now, I'm also not sure under which conditions the protection board resets - cut the cell voltage (or maybe both) or cut the supply voltage maybe even all three things together because then the chip is out of power and it might forget its past.
During first assembly I tested briefly all for me possible faults - different modules having bad contact / or being live disconnected, batteries running empty, baby getting the whole device and use it for playing

- so I thought worst case was tested

.
Latest beginning of next week we will do further testing on T3G's strange behaving device and also check if it could have a bad impact on the connected devices. At the moment I can not imagine, since the TX4Pro and the RX 2 devices have some pretty failsafe linear regulators on its inputs.
Best regards