For some reason, it's often very difficult to initiate the conversation with a bluecap mushroom that allows you to harvest spores or seeds. Unless you find exactly the right angle from which to click the mushroom, your character will just stand helplessly obstructed by the physical placeable. The surrounding terrain sometimes makes finding the right angle downright impossible.
I'm not sure how to fix this but I'm sure everyone who's ever tried harvesting bluecap mushrooms knows exactly what I mean.
They can be tricky. Note to people planting these: Don't cluster them close together or plant them near walls or terrain features. They're big sturdy mushrooms and need open room to grow! At least enough room to walk a circle around because of pathing.