Hope that it is either summer, fall or winter. When the harp is steady or contracting it breaks strings less frequently. Breakage due to tuning can most often be from not noticing than you are plucking one string and tightening another. Tricks on tuning consist of applying pressure on the string, away from the tuning pin as you tighten the string or to first back off the pressure on the string slightly before you raise it to pitch. The reason for these two things is that the tuning pin is hard and the harp string is relatively soft.
Time is long and causes an indentation of the bridge pin into the string.
On the heavier strings this causes them to get stuck on the bridge pin. If the string is stuck the tuning pin will pull on the short length of string between the bridge pin and the tuning pin without the string sliding over the bridge pin. This huge increase in pressure will cause that short section of the string to break. Because of the above discussion, strings are fragile and not warranted. Song of the Sea, Inc.