The /tp command, which comes with an option to cause failure if the target's hitbox will intersect with a block, will treat stairs as a full block and deny teleportation, even if the entity will only arrive in the open part of the stair.

Steps to reproduce

1. Place a stair block on the floor.

2. Walk the player onto the first step, so that the feet position is in line with a bottom slab.

3. Run the command /tp @s ~ ~ ~ true.

Expected behaviour

The command will complete successfully (indicated by a message in chat if the gamerule sendcommandfeedback is true). This is because the player walked onto the stair, hence the position must be clear of obstructions.

Observed behaviour

The command fails (indicated by red text in chat). The bug occurs with various kinds of stairs.

EDIT 2:

Forgot to run with checkForBlocks true in first edit, this bug was reproduced.

EDIT:

Leaving and re-joining the world fixed this issue (tested with oak stairs in all 4 directions), cauldrons, composters and hoppers also had this issue but this was resolved.