Are you using nylon or gut for that string? If it’s always breaking at the same place then maybe there is a rough spot on the prong that touches the string.
Baring extreme weather changes I never break strings. I have broken one string in the past 15 years.
So I would have to say No, it is not typical to break the same string every month. If you can’t find what is causing it then have a professional tech check it out. There must be something wrong with the harp.
Even if it were a weather issue I would not expect it to always be the same string.
I have a similar problem – I bought my harp last November and that F has broken a few times, also that G. But I break strings all the time – I must have broken at least 15 since then… nylon at the top, gut in the middle. Its worthy to note that my strings have been breaking all over and I have broken a string of every type, including metal. Most seem to happen at the disc for me as well – it may be a regulation problem. Also, is your harp new? New harps tend to break strings for a while until they are broken in. Maybe you should experiment with the humidity in the room… you never know what could be affecting your harp!
I noticed that most of my breakings were happening as I engaged the disk – so the pegs would tighten the string and it would immediately break at the pegs. Actually the harp I bought in November was made in 2001, but like your harp it wasnt regularly played, (and that’s why the owner sold it) so when I came along and started banging out a few hours a day the harp had to adjust. Also, the strings didn’t start breaking until months after I got it… not really until this May.
Sam, I’m pretty sure there is something wrong in how you are installing your new strings. You are making the wrong kind of knot, or making the string much too tight so it pops as it goes into pitch. Or, your discs are moving way too far into the string. Have your teacher look at it. I suggest you take it to your next lesson.