I had a mucoid plaque discharge after taking psyllium also BUT I disagree strongly with your conclusion.
If it was the psyllium causing it then you would get a mucoid plaque discharge each time you take the psyllium.
This does not happen.
It happened to me once I thought maybe it was the psyllium like you but then I was unable to duplicate the mucoid plaque discharge by taking psyllium again.
My conclusion was that the psyllim I took dislodged and pushed the mucoid plaque build up out of my intestine.
In other words dont spend $100 on a Colon Cleanse product just take a good dose of pure psyllium.