"NBT tag SkullOwner was of wrong type" console spam, paired with server stalls

Running Spigot #1443

I'm seeing many instances of the following in console:
Looking at the last 13 hours of the server log, there were 12,000 occurrences of this message.

Large batches of them at once seem to result in long server stalls which result in all players being kicked.

Is this the skull conversion? I saw that it has been made async prior to #1443, which I was hoping...

"NBT tag SkullOwner was of wrong type" console spam, paired with server stalls