if i remember right, the previous "can't move bug" which was caused by the wrong centerpoint in client limits the movement of mobs too. What im trying to say: it seems your rmap is too small, everything in the area you describe was outside that "old movable area"
try to reconfigure your rmap (suggesting its a clean "free move everywhere" 1024x1024 map) and set it to brushsize 1.5 in the config. that should increase the size of the rmap and then cover the area that is missing (as 1024*1.5 is the size of our map)
Code:
Map Width = 1
Map Length = 1
Submap Width = 1024
Submap Length = 1024
Pixel Size = 1.5