I had a new 24' sidewalk poured last May that was "cut" into 8 3ft each
blocks. I just noticed that in 2 of the cuts there are cracks the
entire width of the block.

Did the contractor mess up when he poured this by putting too much
stress on the blocks by not leveling it properly?

Also, what should I do about this? I'm concerned that water will get
into the cracks and cause additional damage.

Thank you!