Whilst it maybe the case that the roads in the islands and objects could be the cause , it maybe a good idea for epople to post here exactly what they have tried so that all causes can be eliminated.
As people will already know there are several hundred variations for setting up a convoy and moving them.
Some of the parmaters that can be tested if not already are.
1 . set up the groups ranking sytem properly so they know where they are in a formation and not only by order of wich they were placed in the editor.
2. try all variants of waypoint , safe , careless etc.
3. if way points wont work because of the tightness of the roads or clutter of objects. try domove command in a script and set the waypoints by script.
4 as well as above you can use domove by placing cones on an empty map where you would normally place the waypoint. save the mission and extract the XZY from the mission .sqm rea arange this to X,Y,Z and use domove xyz.
although this may seem silly ,this wil give future readers of this thread something to look at and will also strengthen any bug reports that need to be sent to BIS.
hope this sounds as placid as i am writing it
.
experiment , learn and ,ost of all have fun .
DB