The reason the items are gone is because they haven't been saved to the world yet.If you save your world prior to putting suspect items in furnace, they will be there when you log back in.
When manually adding coal into a furnace while furnace is empty, this repros for me.
Removed all resource packs, still 100% repro when adding 58 coal.1, 3, 5, 7, 10, 15, 20 amounts of coal - all crash and repro.
I've added my crash log to the bug
SunwolfNC
The reason the items are gone is because they haven't been saved to the world yet.
If you save your world prior to putting suspect items in furnace, they will be there when you log back in.