Terrain Changes after reloading in World Builder

[uff1ee]

I've been messing around with this map https://forums.civfanatics.com/threads/map-my-huge-19-civ-map-for-v-25.247328/ and getting it to work with MoM with the additional features. I have a basic version (spawn locations, some barb cities etc) working, but I've encountered an issue when reloading the map, both through world builder and as a scenario, the terrain gravitates towards a plains and jungle filled world. Land, water, and resources remain consistent. Pictures are from the north-east, Umbrawood, at the Svartalfar spawn point.

I originally used MapView to set up the basic map and added the teams/civ/map settings manually (copy and pasting information from created maps).Climate is set to temperate,
top latitude=90 / bottom latitude=-90, same as original map - the only things I can think of that would be causing issues.

Is there some deeply embedded part of the mod that could be causing this problem?

Thanks for any help. Amazing mod by the way.

Edit: Did a little investigating. Found the original file I saved in MapView and loaded it up in Civ IV. Civ made the same changes to the map upon loading. Doubled checked the original file in Notepad++ and it lines up with MapView. I saved a copy of the edited file in Civ and opened it up MapView and Notepad. Both displayed the changes Civ made to the map. Issue seems to come entirely from loading the file into Civ.

Edit 2: Created a custom game and changed everything to grassland, saved the file and loaded it. Same thing happened. Tried again, custom game and saved the scenario without any modifications, same thing happened upon load.

Edit 3: Reinstalled the mod to see if it made a difference. I checked if the would load properly with each part of the install. It seems to break with 2.11. Also found another person who tried a similar thing with the above map, downloaded their copy, and it has the same issues with 2.11 onwards.

Edit 4: Found a solution. In case anyone is looking to do something similar and is encountering this problem: in "..\Master of Mana\Assets\Python\CustomFunctions.py" there's are sections "#create Marshlands" and "#create Plains". Setting the iChance to 0 (4 entries) seems to solve the problem, though I'm unsure if it'll cause other issues. Still have other issues with it changing the variants of forests, but they're minor. Not sure why it stops the jungle spread. I'll update this if I find issues caused by these changes.