I am experiencing the same problem.
In a test data set (70 orders) I increased the distance cost for the route and this fixed the problem. (The default for time cost is 1 and the default for distance is null. I set the distance cost to 1).
I theorize that by telling the solver that distance cost is important, it tries to reduce the amount of overlap.
However, when I increased my data set to 250, the same problem appears even with the distance cost set to 1.
I tried some tests by setting the distance cost much higher (2, 100, 1000, 10000) and this does not resolve the issue.
I am currently looking into this further and will post back if I find any additional information but I wonder if you were able to solve this? I wonder if anybody has some advice?
I'm on 10.3 Advanced.
Thanks!