When trying to build while shifting it's as if you are in spawn protection (taking the blocks away but not placing them, if you move the stack the number will go back to normal again)
when you don't shift you are able to place blocks

I was using a sign when the crash happened on multiple occasions
This happens 3K blocks outside of spawn as well, so far other blocks do not seem to crash the server but also display this "ghost placing" effect when shifting