I have found map that leads to buried treasure. The location of chest was chunk generated before any snapshot of 1.13. There was no chest at specified location. (I have also checked /locate and dug a hole to bedrock).
After regenersting world, there is a chest at coordinates given by /locate.
The generation of a treasure map doesn't neither check the existence of a treasure chest nor does it generate the chunk with the treasure chest.
The map and chest are generated independently from each other.