When you save the game on a glass block in the Nether(only in the Nether not in Overworld) using some configurations, after you reload the world you will spawn in on a nearby solid block on the same y coordinate instead of on the glass block. This only occurs if the x coordinate of the glass block is less than the x coordinate of the solid block, and occurs with 99% consistency. I know it sounds confusing but follow my instructions exactly(same coordinates, same blocks) and you should be able to replicate it. There are many builds that can get it to happen.

How to reproduce
Step 1: Create a new world in creative mode and go into the Nether
Step 2: Build a structure just like below, with the yellow glass on x coord 1 and the iron block on x coord 3. Blazes are optional.

Step 3: Go onto the centre of the yellow glass block and save the game.

Step 4: Reload the world.

Observed results:

The player spawns in on the iron block, in the middle of the blazes.

Expected results:

The player should spawn in exactly where the game was saved, that is on the yellow glass block.

I'm using Android 10, and this happened to me on my own singleplayer world. No idea if it happens on multiplayer worlds or other devices.