Some blocks do not respond correctly to getHarvestLevel - I find that it is mostly the various Stone based blocks, having no proper harvest tool.

This is also true for Crafting Benches, and probably other wooden blocks. This is especially serious as you cannot extend ItemAxe, and thus cannot use Block#getHarvestLevel to check if your custom axe can mine a block without risking mod incompatibility.

Be more specific, what blocks exactly.

 

dispenser

noteblock

bed

brick_block

mob_spawner

oak_stairs

chest

crafting_table

furnace

lit_furnace

standing_sign

oak_door

spruce_door

birch_door

jungle_door

acacia_door

dark_oak_door

ladder

stone_stairs

wall_sign

iron_door

oak_fence

birch_fence

jungle_fence

dark_oak_fence

acacia_fence

trapdoor

stonebrick

brown_mushroom_block

red_mushroom_block

iron_bars

oak_fence_gate

spruce_fence_gate

birch_fence_gate

jungle_fence_gate

dark_oak_fence_gate

acacia_fence_gate

brick_stairs

stone_brick_stairs

nether_brick

nether_brick_fence

nether_brick_stairs

enchanting_table

brewing_stand

cauldron

end_stone

double_wooden_slab

wooden_slab

sandstone_stairs

ender_chest

spruce_stairs

birch_stairs

jungle_stairs

cobblestone_wall

anvil

trapped_chest

light_weighted_pressure_plate

heavy_weighted_pressure_plate

daylight_detector

daylight_detector_inverted

redstone_block

hopper

quartz_block

quartz_stairs

dropper

stained_hardened_clay

iron_trapdoor

hardened_clay

coal_block

acacia_stairs

dark_oak_stairs

prismarine

sea_lantern

standing_banner

wall_banner

red_sandstone_stairs

double_stone_slab2

stone_slab2

chorus_plant

chorus_flower

purpur_block

purpur_pillar

purpur_stairs

purpur_double_slab

purpur_slab

end_bricks

Right these are all material based things.

Which its on the item's end to determine if they have a harvest level.

There is no way to generalize all of these values, your item just needs to check the material in canHarvestBlock which is delegated to when the block doesn't have a tool.