The byzantine mission "Breadbasket of the World" replaces the nile goods produced modifiers with more powerful versions. The next mission "Aegyptus" then allows you to release a historical friends mamluks subject in egypt. Releasing this subject completely removes the nile modifiers, as is typical of most normal province modifiers, but since the modifier replaces the normal static one this effectively permanently nerfs the nile for the rest of the campaign.

Oh also my mamluks spawned with "no religion" as state religion. Just an extra minor nuisance.