I know this post is from awhile ago, but I’m just curious if you ever found out the cause or reason to this? I have the SAME exact problem, where everything is still regular and normal EXCEPT the fact, I keep getting the first quarter- third of the stool is hard pebble like pieces stuck together and then the rest of the stool is normal. and am too worried about a blockage, tumor ect interrupting the flow of normal motility.
Iv tried ALL the typical extra fiber, excercise, drink more water ect tips nothing seems to work or change this.
Did you ever figure out what this was?? Or why it happens