Did you know you can use curtains to make blocks disappear? I don't think this is intentional, and i don't think you can get those blocks back. If you place an item against a window, then close the curtain on them, it causes the item to vanish forever. I had a raccoon in a cage and went to close the curtain and it just disappeared. Is this possible to fix? Maybe not allow the curtain to close if there are items blocking? I was testing how curtains worked and didn't realize the curtain placed on each side would fully extend on a fairly long curtain rod. To my surprise, as well as the caged raccoon's surprise. He vanished. I opened the curtains and placed another block against the glass slab (maybe a block of wood. i forgot) then did the same and that block vanished too. Perhaps the raccoon and the wooden block teleported to a better place.
I am playing version 1.15.5 and using 1.4.13 of this mod. I didn't upgrade because I didn't think the mods after would be compatible with my version of VS. However i never saw this issue addressed in the notes either.