The solution is supposed to have a pH of ~ 4
No, that's not expected pH for KCl solution.
If prepared with distilled water and kept in an inert atmosphere, it should have pH close to neutral (not exactly neutral, K+
reacts with water acidifying the solution a bit, plus there are thermodynamic effects). If allowed to equilibrate with air (containing CO2
) pH should go even further down down and stay somewhere between 5-6 (due to the creation of the carbonic acid), but it won't go lower.
No idea why the pH is higher - but there is always a chance water or salt are contaminated.