How to handle ground and neutral in multi gang box containing both branch and traveler further down on same branch?
I'm guessing your wiring looks something like this.



So if you also draw the grounded (neutral) conductors, it looks something like this.



Drawing it like this you can clearly see, if you connect the grounded (neutral) conductors in box 5 (B5) to the grounded (neutral) in box 1 (B1), you'll have a giant loop.

It shouldn't cause any problems, electrically speaking. Your electrons will just be able to take different routes back home. However, as ThreePhaseEel points out, paralleling conductors in  this way would be a code violation.  To avoid paralleled conductors, you should wire the circuit as shown in the second image above. Notice that the grounded (neutral) conductors are kept separate from box B3 on.