Thank you for the reply.
The 25A ESC worked well with its own governore, but refused to let the Spirit unit govern him
I tested a HW 40A version 4 and it let the Spirit unit take over and started as soft as it should.
Since the ESC was identified as the "bad guy" I flashed the firmware of the 25A Hobbywing with the current, up to date version.
This firmware was already on the ESC, but obviously corrupted
Now this ESC does also work fine again!
I'm very happy, that the Spirit unit is fine and as allways NOT guilty