When Bone Meal is in a dispenser, it is detected by comparator but the dispenser isn't able to throw it
Linked issues
duplicates 1
Comments 3

Along with a video, please properly define what you mean by 'throw' in your case. If you expect the bonemeal to be dropped out as an item if it cannot be used, this would be intentional behavior based off of MC-109400. Droppers should be used if you want to drop bonemeal as an item,
I wasn't aware of this functionality, it work well now with the dropper
Please send a video of this issue occurring with the debug (F3) screen open.