A10 Pro + 3dTouch + firmware problem

[papchristos]

Hello all,
Posted this issue at the facebook pages too, but perhaps some good answers are found here.

My problem:
After installing the 3dTouch and flashing the firmware on my A10, the bed levelling goes well for the first 7 points, but the nozzle crashes on the bed at point 8.

My machine:
Geeetech A10 Pro, with a GT2560 v4.0 board, running Marlin 1.1.8 .

My process, problem and search for solutions:
I physically installed the 3dTouch without issues. I then flashed the firmware through this page: https://www.geeetech.com/download.html?download_id=30 . Here, I got the "A10_G05(CH340 Support 3Dtouch)" firmware, because it seemed to be the one for my v4.0 board. Flashing the firmware went fine, and so did all basic commands (moving the axes, homing the head, testing the 3dtouch, etc.).
HOWEVER, when actually attempting to level the bed, the measures are done perfectly for the first 7 points, but on the 8th (center back of the plate) the nozzle crashes on the bed.
After this problem, I checked the "About Printer", then "Board Info" setting: the firmware seems to have now gone back to "v3.x", no longer v4.0 as it was with the previous firmware. So, was the firmware above the wrong one?
When looking for more firmware resources, I came across the Geeetech forum page https://www.geeetech.com/forum/viewtopi ... 20&t=17046 , which suggests a series of other Marlin firmware upgrades, but none of which seems to match my v4.0 board.
I have also tried disconnecting the z-stop: no change in the behaviour above.

I am at a loss! Is it a firmware problem after all? Is it rather a faulty sensor, or something I can fix myself? Your help is very much appreciated, thank you!