Turns out that big piece was a giant ball of carrot. I may have to take carrot off the menu just because it was so dry it was hard in the cockroaches digestive tract.
Yes it does look like the pieces of carrots cause a blockage of the cockroaches digestive tract. You have a smart mantis that knows if the cockroach could not breakdown the carrots neither can he.
There’s been a lot of internet discussions surrounding carrot fed crickets as a food source for mantids. It might be a legit concern or it might be an urban legend.