I Don't Know Why But I saved a new String Name for my structure. (Probably because I may have forgot the old string name.) and I go to a test world. When I place {/Structure load D-House1 ~ ~ ~} I get an error message saying that Minecraft didn't find a string name for D-House1 although I may have saved a new string name for it minutes ago.

P.S also I found this in 1.16.221. But idk if it works at the 1.17.0.56 Beta.

there's proof you may see that it's happening.