How to replicate it:
Get a non-full block such as a torch, slab, flower, ect. and place red sand several blocks above it or pile up red sand above it and break the bottom red sand. When the falling sand breaks, a normal sand item pops out instead of a
red sand item.
(The red sand in the screen shoot are the pieces I broke manually)
(Sorry if this was already reported, the search was not working)