As a dietitian; here are some unusual side effects of eating excess fiber;
May lead to nutrient deficiencies
Getting more fiber than the daily required value can inhibit the smooth absorption of essential vitamins, minerals, and other nutrients. The excess fiber tends to combine with some minerals making it harder for the nutrients to be absorbed in the bloodstream, resulting in a decrease in the long run.
Can cause bowel obstruction
Eating too much fiber can increase your stool weight and size as it binds with undigested foods and other nutrients, triggering bowel obstruction. This can make it harder for frequent bowel movements.