[1.12.2] Pathfinding bug: tryMoveToXYZ() missing destination

I'm trying to make mobs follow a line of my mod's "sugar dust" blocks, clearing them away as they reach them. (The sugar dust blocks are, for all intents and purposes, identical to redstone dust in their collisions, passability, models, etc.)

I have this AI class, which I'm inserting into EntityCreature task lists in the EntityJoinWorld event: https://github.com/IceMetalPunk/Placeables/blob/sugar-placeable/src/main/java/com/icemetalpunk/placeables/ai/EntityAIFindSugar.java

It's basically just a BFS to find the nearest sugar block in range, then it uses the built-in navigator to pathfind to it.

It works about half the time; the other half, the mob pathfinds to the block *next to* the actual sugar block instead of the sugar block itself. That causes it to get stuck, since it never clears the sugar and thus keeps finding it and pathfinding back to the current block.

So my question is: if I'm passing in the sugar block's coordinates, offset by (0.5, 0, 0.5), as the destination for the navigator, and the sugar block is passable with no collision mask... then how come half the time the mobs won't actually land on it?