Saved structures files, loads back almost empty or recursive

Opened a new World in Creative, superflat, Peaceful mode, no mods or any other fancy graphic … anything.

I imported some houses from another world, using a Structure Block and modified them to add some of the new blocks.

I then saved them with the same structure block (changing just the name of the file, same size): See an example in one of the images

In order to check them I loaded them back, with the result in the other image.

In 26.4 snap 6, the load result was a single red wool block (the first near the structure block), all the correct loading area empty.

In 26.4 snap 7 (just tried), the result is even more strange: instead of 1 block, a line of blocks (from the first line of blocks), but repeated twice, indented, structure block included.

I really depend on these structure files so I hope that it will be fixed someway.