Issue

If you have a structure block on save mode and include entities on and then save it by putting a redstone block next to it. If you then open the structure block and switch to load mode. Now put a new redstone block next to the structure block and it will load all entities and blocks as expected. But now you do /reload (or leave and join world) and power the structure block again and now you see that the block and entity dont get loaded!

Now do the same again but instead of saving it by a redstone block you open it and click on save button now after you /reload the blocks and entities still get loaded!

 (Bug verified in 1.17)

Video example

Minecraft structure bug - YouTube