As it is now the creatures reset their animation after reaching a new waypoint node. To prevent this a new spline has to be sent to the client while the old one is still running. My old project was based on an AzerothCore fork from 2020 which was itself based on SunwellCore. They fixed this by starting a new spline 200ms before reaching the next node, which prevented the animation "hiccups", but was only a workaround. CMaNGOS seems to have implemented a better solution by sending a new spline 1.5s before reaching the end of the old one and ensuring that a spline is at least 6s long by including multiple nodes if necessary:
https://github.com/cmangos/mangos-classic/blob/master/src/game/MotionGenerators/WaypointMovementGenerator.cpp

I tried to implement this in my own project but gave up eventually (well, actually I gave up the entire project recently). Perhaps something similar could be implemented in VMaNGOS.