pic:A BTA would stick to rock work, they don’t like sand.
If he was an LTA, then yes, he would bury in the sand, but not upside down.
If he’s falling to the sand then flipping upside down, that would certainly indicate a problem.
If his foot was damaged, this would be real bad.
Are you saying that he’s stuck, then travels to the sand bed, then turns over?
Was he bought from LFS or shipped?
What colour is he?
Maybe a pic of him and a FTS might help.