Try not to double post.
I was wondering whether your faction leader and son are in the same army? If they are, then both will be affected by the commanding officer's (your faction leaders) movement restrictions. If you seperate your two characters, then you should find that one of them has better movement.
Apart from that, other than the terrain and climate your wandering through, i cant really think of any game reasons why this should happen. If it persists try starting a new campaign
Bookmarks