Minecraft v1.20.1
Forge v47.2.20
Nether Chested v8.0.3
Quark v4.0-441

Pressing the sort button in the Nether Chest from the Nether Chested mod, if there is any stack over 64, everything but one stack is deleted. If there are no stacks over 64, it sorts as normal.

Reported to Nether Chested as well, see Fuzss/netherchested#22 (comment)

Before sorting:

After sorting: