They'll navigate around the budding amethyst blocks, but stop when running into a larger amethyst bud or full cluster, instead of pathing around it.
It's not a full block, so they could technically shift a little to the side and walk through it, but even considering fully open paths, there are options that they don't consider because they think they can walk through the amethyst buds.

Orange star is where the Starbuncle was sitting, trying to get to the archwood chest, but not able to get through a large amethyst bud (which grew into an amethyst cluster and still blocked). Once the cluster was harvested, it continued on its way.