Thanks @veti & @dc42 for your reply. Highly appreciated to get such a quick answer.
Individual tower moves G1 S2 moves --> OK
Endstop status M119 --> OK.
Increased homing distance from 405mm to 500mm. --> that was it !!!
(I initially thought 405mm would be more than enough, since my homed height is ~360mm. That was my fault)
Thank you both for helping me.
Best
Stephan