The weather modifiers for the ships seem wrong. There are modifiers for Mountain attack, Forest attack and so on in the save game for ships in this mod right from the start. I noticed this because my ships got a -90 modifier for clear defense...
From where does the the scenario load these modifiers? I would like to fix this.
Air and land units seem fine, modifiers.csv in units is ok as well.
Edit: modifiers.csv was the problem. Replacing it with with the one from DH-full removes the bug. This also removes some modded values, of course. (shore attack of land units and a lot of modified values for air units.)
The ships had their movement in adverse weather modified, it seems that doesn't work with the latest DH version (there are no modifiers in the DH full file)