If another move route for the player is set the old move route is replaced.
A dash system where you change the player speed every time is a typical cause.
Look through your parallel processes. (Both map events and common events)
Additionally your Wait for Move's Completion is dangerous if there are any other movement in the area, and it seems to be unnecessary in your situation. Otherwise a wait X amount of frames is preferable.
*hugs*
- Zeriab