In any dimention using /spawnpoint while standing on soulsand makes the game think your respawnpoint is obstructed
edit: does not seem to apply to beds, respawn anchors
MC-175243
/spawnpoint hates soulsand
Resolved
Invalid
0
That's because the command takes your current coordinates by default. Since you sink into soulsand, your spawnpoint is set inside of the soulsand. That block is obviously obstructed (by the soulsand).