Geeetech

Upgraded to a GT2560 A+ board with 3D touch. Everything seems to work ok sometimes, but 3D touch seems not to sense bed correctly. Prints are always tight at the front of the bed and loose at the back. When I watch the printer doing G29, printer goes to home and touches ok, moves to front right and sometimes presses into the bed, even though the 3D sensor has clicked. I have to turn it off quickly before it does damage. When it does sense the front correctly and moves to the back, there must be at least 0.5mm gap between the bed and hot tip.
Any ideas??