Changing the monsoon strength on line 461 and then running it as a local mod seems to improve things.

vNormal = lerp( vNormal, vMudNormal, saturate( vMonsoonStrength * 2.0 ) );

So far I've only tried changing it from 2.0 to 0.4 and it makes the area look a little 'muddier' rather than being black. It looks ok to me but it may be possible to make it look better by trying a few different values.

It's worth mentioning I know nothing about creating a mod, and I've only worked this out by comparing other mods and doing a bit of trial and error, so I can't guarantee improving the monsoon problem will not create a new issue with something else. But after a few hours testing it seems ok for what hopefully will be a short term fix.

Good find Varlin, this workaround seems to be working fine for me after a few hours testing.

Playing around with this a little bit, replacing 0.70 with 0.00 in the line below can remove the monsoon graphical effect entirely rather than just tone down the mud:

float visMonsoon = lerp( vFoWColor.b, vFoWColor.g, vFoWOpacity_Time.z ) * 0.70;

Might be possible to further tweak both lines to get just the right amount of monsoon effect to suit individual preferences.