I have no idea, but is it possible that the lack of fiber can cause an illness, and that adding fiber at that point can make symptoms of that illness worse, once it's taken hold?
Yes, you can get inflamed from constipation and bacteria screwing with you and such, and then insoluable fiber and other material that doesn’t digest can cause more irritation, but I’d argue the biggest problem with fiber might not be fiber itself but the foods that have fiber in them because they all tend to have FODMAPs which are also implicated in ibs/ibd.
Fiber I believe it’s generally recommended you take as much as you can if you aren’t having issues.
Fiber I believe it’s generally recommended you take as much as you can if you aren’t having issues.