depends on how fond you are of the terrain!
try an experiment --and this WILL be a lot of work (and that I mean!).
rename & backup the original movements ini, and create a new one. keep the upper section, as that defines the 'front line' dividing red & blue exmaple (from Waterworld):
[FrontLine]
FriendlyBase=Levu Vana
EnemyBase=Gavabutu
Position[001]=467511,552932
Position[002]=545958,512183
Position[003]=587163,512770
Position[004]=600237,536868
StartShow=1
EndShow=5
delete all the other routes
have at least 1 each, for both sides,
shipping routes
truck routes
ground attack routes
keep them near the middle 2/3s of the map.
see if the problem persists.
like I say, this is a random f***up that just been appearing (to my notice) over the last 4-5 months (or I just was too selfinvolved TO notice it before!) And it's only on 3rdparty terrains. Which leads me to belive it's in an ini somewheres, as opposed to a dying terrain engine dll or other core file.