How to deal with a professor skipping his office hours? As a preface, this is a related question but it is from a different perspective. 

I am an undergraduate student in physics and have a professor that routinely ignores his own office hours. He has three scheduled office hours/homework help sessions each week (two hours on one day and a third the next). 

The professor has (and has had all semester) a known staff conflict during the second hour of the first help session and as such has missed at least one hour every week. He has not and will not reschedule this hour. 

He also is routinely late to the first hour on the first day as well. As such, he is only at his office hours for twenty or so minutes for the first session. The second day he holds office hours he also often comes late but is much more consistent in attending. Unfortunately for me, I have a class conflict at that time and can rarely attend. 

As a student, I learn best while working on homework problems and in one-on-one (or small group) interactions with the professor. Because of his unavailability, I feel like I am not learning anywhere near as well as I could. This is extremely frustrating to me as a student and overall I would like to know what, if anything, can I do as an undergraduate student to encourage my professor to attend his office hours?
Most faculty members state that they are available during their scheduled office hours or by appointment. If this is the case, then the most effective way for you to handle this situation is to send an email (or in-person) request for a short meeting outside of the regularly scheduled office hours.

If the request is declined, you may want to speak to the person in your department who is responsible for undergraduate education to let them know about the situation, and ask for help in resolving the situation.