Saving of structures works, until you end your game session. You will find no structure saves in the level folder. On the next start of the world you won't be able to spawn your structures.

What I expected to happen was...:
I expected, that structures with names like "minecraft:lecture0", "minecraft:lecture1" and so on will save successfuly.

What actually happened was...:
Saving and loading of structures worked only in single game session. After world restart it didn't work. I found no structure saves in my level foulder, except the first one (lecture0.nbt), but it doesn't work in game.

Steps to Reproduce:
1. Create a building
2. Save it with structure block (my name was "minecraft:lecture0")
3. Load it with structure block (<- it works)

4. Go back to the main menu
5. Load your world again
6. Try to load your structures with structure block