If you pick up items when creative inventory is open, the items do not appear in survival inventory.
Steps to Reproduce:
In creative mode, fill your hotbar.
Stand on the ground and face down.
Drop items from creative inventory.
Pick up them without closing creative inventory.
Open survival inventory and check if the items you picked up are visible.
Observed Results:
The items you picked up become invisible.
Expected Results:
The items should appear in survival inventory normally.
Notes:
It also can be done by opening creative inventory when you pick up items with a dropper or something.
If you interact with something such as a chest, they will be visible again.
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@Avoma You have to fill only your hotbar before picking up items. Also you should drop items from creative inventory, not the hotbar.

Can confirm as of 1.18 and 1.18.1 RC1

Still an issue as of 1.19.1

This seems to be related to MC-3263
I believe this is a duplicate of either MC-8409 or MC-170863. Apologies in advance, I'm not too sure.