I can now confirm that in 1.13, this has been resolved.
Another update; this is still a thing in 1.13. Again, not present in 1.12.
Just wanted to update that it still happens in 1.13-pre7.
Ah. Well, I hope they do. 🙂
Have you now found the culprit to this problem?
No, 1.12.2 works normally.
Hi Kumasasa,
I have now uploaded the log file.
My apologies for not originally including it.
I can confirm this.
I've explicitly rendered a deep ocean map, and explored over ten wrecks and probably just as many ruins.
The chests that once contained treasure maps now simply contain empty maps.
I can use Discord with Minecraft 1.12 without issue. This bug is only affecting 1.13 and its snapshots, and it happens whether I have Discord or Skype open, or not.