With that much water in your recipe (just over 27% lye concentration, which is a lot of water for a predominently olive soap), it would have gone into gel fairly easily. Coconut tends to gel fairly hot, so the combination would mean that your soap was probably ready to cut many hours before you actually cut it.
Without making any suggestions on the recipe itself, I would suggest to you that you use a water amount that is somewhere between a 30% to 33% lye concentration (and move away from lye as a percentage of oils - this leads to fairly unpredictable water values and a water amount that is too high for olive based soaps) for future recipes.
For cutting, when the soap is no longer easy to dint if you push on it with your finger, then it is ready to cut. High coconut soaps tend to need cutting when they are warm, they harden up so much and will crumble when they are cold (not sure whether the percentage you used would cause this effect, but it's worth knowing this can occur with coconut soaps).
Cocoa butter does cause brittleness, but I like it in soaps (and have used it at the concentration you have) ... just cut before the soap is too hard and you will be ok.
Crumbling can also occur when you cut too early (when the soap is still fairly soft). This is more often a problem with ungelled soaps, but for gelled soaps, using the finger test (until you get used the timing and look of your recipes) to test the hardness of the soap will help you increase your understanding of what texture/hardness is best to cut at.
Ultimately, the thickness of the blade has pushed the bottom edge of the soap away from the surface because it's easier for the soap to crack and break than for the soap to move away from the blade as you slice through (it's not much of an effect - this would happen more with a wedge shaped knife). If you cut when the soap is at the "right" texture - not too soft, not too hard, the crumble won't happen with that blade. A wire has even less of this effect (there is even less soap being pushed around when cutting with a wire).
It is not terribly noticeable on your soap. If it concerns you, you can tidy it by bevelling the edges with a peeler (or similar)