the seed i used to find this is -2135181137524156350 and the boat i found with this issue is; -1429 61 800 ( it spawned under a beach )

how to replicate:

1, find a boat

2, right click on a chest that can spawn a Buried Treasure Map and wait a few seconds as it take awhile for it to open

3, it will look like a empty map but will have the special Buried Treasure Map name on it.