One thing I tried and worked ...
When you don't find the stud...look on the wall on the other side and get some measurements.
Then if you are concerned about holding power,,,just squirt some construction adhesive into a larger hole you drill at the edge of the stud. Drill the hole where it will be covered by the base of the bar. Then when the glue dries inside the wall ...it is into something solid ...which is attached to the stud.
I use PL 400...apply a little to the back of the bar too. But not so much it gets all over.