I also have the 2.4 board, but have no problem probing (even with the original board that came with the machine), but I do not use the same commands that you use because I ALWAYS got an error.
Actually I always had difficulty using the commands that are listed (Similar to your) and somehow, somewhere on some forum I found this information about 8 months ago that helped me (after hours of searching)
First I HOME my machine, and CLEAR any offsets. Next, I rapid over to my part, (I usually like to set my Z first) and stop the cutter about 1/4 (6mm) above the area I want to probe for my Z. I then look at the Z position on the left side of my computer screen. Let's say it says -46.00 mm. I then type
G38.2 Z-56 F15 (The number -56 is not critical as long as it is great than the distance to the part less the present position)
The Z will then travel down to the part and stop
If I put a number that is too small to touch the part, say -50mm, it will travel down 4mm ( -50mm -46mm = -4mm) and then I will get error Alarm Probe Cycle Fail (because the probe did not touch the part).
I then probe the X and Y making sure that the number that I type after the G38.2 command (X or Y direction) is greater than the distance to the part.
Let me know if you have any questions. I have a Probing Video on my YouTube channel that also my help (Search RichardCournoyer of Shapeoko Probing)
I use the probing command almost every day....
My machine probe setting is: