Hi, thanks for the replies,
I replaced the breaker and it seems to have solved the issue, no trips after a day of heavy HW use. The one I took out looked to be quite old ~10+ years, and the new one is not heating up like the old one.
Before I replaced the elements we went a month having to constantly reset the HW heater after hitting the limit, I think that time was especially hard on the breaker. So hopefully this issue is now solved.