As the messages issued, your time step interval of 0.1 second may be too large. Please try to use smaller value.
I guess that the winding in speed is -1 cm/s instead of -1m/s.
Please also check if the mooring attachment point is along the vertical line acrossing the structural COG. It may be pssoble to deactivate all DOFs motion except heave.
To lower the block from the water surface, the paying out speed should be positive, and the final length should be larger than the initial length.
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