Guitar high-pitched strings are boring.

The tension of the new string is relatively high, that is to say, the string has not been opened yet. After being adjusted, let alone leaving in two days. After playing for two hours, the timbre will be inaccurate, because the strings haven't been opened yet. You need to adjust the standard tone again and repeat it several times. When the string is completely pulled apart, it won't happen again. This must be the reason, because every time you change a new string, it's your situation.