I loaded into a world and the treasure map showed treasure
a. Under the water (quite a way)
b. Dg around (You need to look lower than the map tells you I found it using fill command to get rid of gravel)
c. The location was not under sand but under gravel and stone instead
To experience:
Use seed -4786893271456824633
Go to the above ground ruins
Follow the map
Try to find where it tells you
It does not generate sand around it, it takes whatever block it replaces, and generates that around it. It is just usually sand, as buried treasure can only spawn on beaches.
Works as intended.