When typing /spawnpoint on certain blocks, the game will say your home bed was missing or obstructed. This happens because spawnpoint is based off the block coordinate and if anything is there that is solid it'll spit out the message. Even blocks that are a pixel short will fail. The blocks that are affected by this are:

-Grass path
-Farmland
-Soul sand
-Honey block
-Lectern
-Composter
-Cauldron
-Stairs (all variants when on lower step of stairs)
-Slabs (all variants)
-Chests (all variants)
-Lantern
-Hopper
-Brewing stand
-Cactus
-Bamboo (when standing on same block)
-Turtle eggs (all sizes)
-Trapdoors (all variants when on ground and open on wall, flush with ground will work)
-Empty end frame (end frame with eye of ender will work)
-Doors (All variants when inside same block as door)
-Stonecutter
-Campfire (lit and unlit both don't work)
-Glass pane (when in same block)
-Iron bar (when in same block)
-Conduit
-Cobweb
-Fence gate (all variants. Works when standing on top, not inside the fence)
-Fences (all variants, work on top but not side of block)
-Daylight Sensor (both variants)
-Water
-Lava

Blocks that work that surprise me are:
-End rod (even on the side of the block and if the block is sideways)
-All heads (any position)
-Magma block
-Slime block
-Lily pad
-Ladders
-Vines
-Snow (all levels)
-Carpet

Work around:
Place a full block beneath the player and type /spawnpoint. Replace the block with the none full block and the player will spawn on top. I'm trying to have players spawn on paths so this is what I'm doing.

A few of the blocks I listed seem intentional whereas some others do not, I figured I'd list them all just to get the cards on the table. Thanks for taking the time to read this.