In all my jobs where I use Git Parameters (used to select branch/tag for several repos), my build number increments by 2 (and in certain cases increments even by 3 or more)
When Git-Parameter is not used, build numbers increment always by 1, as it should.
I have seen many related issues, which are now closed, but they are not actually fixed as I'm facing the same problem.
Reproducing it should be easy. Just create a pipeline job and use Git-Parameter (I use two Git Parameters in my job)