Seed: 5450957878814971038
/tp @p -1800.287 12.91045 -144.444

How to Reproduce?
1. Install snapshot 21w2a
2. Open Minecraft
3. Create a New Word with the specified world seed
4. Open LAN and enable cheats
5. Switch to Spectator Mode
6. Use this command -> /tp @p -1803.093 12.91045 -142.585
7. Switch to Creative Mode

There is a chance that mobs such as Glow Squids spawn inside the block when chunks are loaded while in Spectator mode.

Additional notes, mobs in spectator modes does not move in accordance to the Minecraft Wiki.

"Mob view

A spectator can click on an entity with the attack button, to take its view. Their position is locked to that of the entity, and their POV moves in accordance with the entity. Viewing oneself while spectating from an entity's point-of-view using F5 shows the entity. Pressing the dismount key (⇧ Shift by default) returns the player to flying mode. In addition to spectating mobs, players can also spectate any other entity, such as an end crystal, primed TNT, or an armor stand.

Certain mobs also apply a shader while looking from their point-of-view. This filters how the world is portrayed to the spectator. Similar to the Super Secret Settings, if one presses F4, it removes the filter without dismounting the mob. Below is a table of mobs that have a filter."
~Minecraft Wiki