I had a look for mentions of "floppy pouch syndrome" to find out the definition, but could only find it referred to in one paper with no explanation.
I did find mention of "floppy pouch complex", which was defined as:
"Floppy pouch complex is defined as the presence of pouch prolapse, afferent limb syndrome, enterocele, redundant loop and folding pouch on pouchoscopy, gastrografin pouchogram or defecography. Common clinical presentation includes dyschezia, bloating, abdominal pain, straining or the sense of incomplete evacuation."
https://academic.oup.com/gastr...icle/6/4/246/5048415
If this is what your doctor was referring to, then that's not megapouch. A bit confusing, because, in megapouch, the whole pouch goes floppy, but obviously floppy pouch syndrome is describing something different. Sorry!
On the plus side, I believe some cases of floppy pouch syndrome can be treated with revision or repair surgery. (Megapouch can't – the pouch has to be removed and a new one created from a fresh section of bowel, or you have to go to perm ileostomy.)