So today I came across an issue where using /decompress on a compressed redstone was not giving me the full 9 stacks of redstone. My party member recreated this bug a bit later with compressed iron and we managed to narrow down the exact way to recreate it. We held a small stack of the compressed items, and after doing /decompress, we then did /craft to make the items into blocks. After crafting we then did /decompress on the next ones and slowly after each time it returns less and less items. In my case it was returning only 3-4 stacks of redstone, in my party member's case it returned 72 iron ingots. Screenshots below, we included NBT tags and lore of the compressed iron I do not have screenshots of the redstone with that information.
