Saved items in container disappearing

[waltersamson]

Minecraft 1.16.4, forge 35.1.37, WDL 4.1.1.0

Summary:
Sometimes, an item already saved in container in previous downloading sessions would disappear after downloading again.

Currently only observed in barrels.

Rough steps to reproduce:

1. Start downloading
2. Open a barrel with items, close it, stop downloading
3. Go into singleplayer save to verify that items have been saved in barrel
4. Join the server again, start downloading, but do not open that barrel
5. Stop downloading, go into singleplayer, the barrel previously with saved items would be empty.

There is a similar phenomenon with item frames that in a downloading session, if I don't go to a previously saved item frame's location, that item frame would disappear in the saved world.

[Pokechu22]

Sorry for taking a while to respond. A similar issue was recently reported (#238) which found that this happened when going between dimensions (e.g. entering the nether) while downloading; do you know if that was the case for you?