Hello! Yes, I understand what you're saying. I feel really sorry about this; the error occurred because I used the same game item to serve the role of the custom item: the jigsaw block.
This was a big mistake on my part because I should have used a different item (for example, command block, structure block, etc.) since Mojang hasn't provided "dummy" items, so to speak.
I could release an update to fix this and make it compatible, but I have to consider people who are already using the current versions, as updating would render their setups obsolete.
Again, I apologize for not realizing my mistake earlier. It's something that can be fixed, particularly if you go into the texture pack and datapack and replace the jigsaw block with the structure block/command block, etc.