Minecraft version: 1.20.1
Forge version: 47.4.0 (Also tested on 47.3.0 with Iron Furnaces)
Sophisticated Storage version: 1.3.9.1075
Sophisticated Core version: 1.2.23.902

Other Mods:
Iron furnaces 4.1.6 OR GregTech: Modern 1.6.4

Description:
Hopper upgrades void items in Sophisticated Storage blocks when the block they output into is removed.

Reproduction steps:

1. Create a New World with either of the Other Mods above.
2. Place a Diamond Furnace or LV Electric Furnace depending on the other mod chosen.
3. Place a Sophisticated Storage Spruce Barrel atop that furnace.
4. Put a Hopper Upgrade in the barrel.
5. Load up the barrel with Logs (4 or more stacks)
6. Wait for the furnace to fill with logs.
7. Remove the furnace by breaking it.
8. Observe that the logs slowly void themselves over time, as if they were being transported into a container that no longer exists.