This happens so often and makes the unit very unreliable. It isn't them targeting something behind a hill. They just miss the target in a lot of situations. The temporary fix of making it a projectile would be easy to bring back and is used in the non FAF modded game.
Please Fix Rhino missing shots
Could you make a bug report on Github: https://github.com/FAForever/fa/issues/new?assignees=&labels=status%3A+novel+issue&template=bug_report.md&title=
It would allow me to more easily investigate the issue. It shouldn't miss that often.
A work of art is never finished, merely abandoned