You can have mucoid plaque in your colon and it does not appear in the colonoscoy. You need to see a picture with the colon to understand this. The colon has three main parts: ascendant colon, transversal and descendent colon ( many subparts).
The colonoscopy mostly only reaches the sigmoid portion of the colon, not even the descendent colon. So, colonoscopies can not show mucoid plaque.
I have passed a lot of mucoid plaque and I could feel it being loosened from the ascendant colon. I had colonoscpies and they did not show any mucoid plaque.
So, I suggest to follow a colon cleansing protocol.