First observed in a world created in 1.12, on a server.
Server updated to 18w30a.
Killed a few mobs but could not pick up their dropped items.
Can pick up mined blocks and thrown items.
UPDATE: same behaviour observed in a single-player local world, followed by a crash.
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Singleplayer world upgraded from 1.12.2 to 1.13, played in 1.13, does not exhibit this issue.

Yes, it's MC-134816

MC-134816 doesn't mention not being able to pick up, and in my case it does not always crash. I think the not picking up is a separate issue.

Reproduce:
Setup Command block to spawn cows:
[media]Spawn Cows:
[media]Kill Cows:
[media]SOME Items can't be picked up:
[media]++ Confirmed in 18w30b
Can you confirm this too when upgrading the world from 1.12 to 1.13 ?