Agreed - check the test kit first. However, it is possible to have slightly different morning/evening readings of kH. If you are not using a pH controller, but injecting CO2, you will have a changing CO2 reading during the day. For instance, if your CO2 level is at its highest in the morning then your pH is at its lowest. Since a kH titration uses an acid to lower the pH, it will take less when there is more CO2 in the water - an apparent lower kH. If at the end of the photoperiod much of the CO2 is exhausted (and a higher pH) then the apparent kH will be higher.
Bottom line: if your starting pH of the sample is different due to CO2 levels, then the kH reading could also be different. Not by 190ppm, but the lower the kH the more significant the error. For low kH samples, it is best to let the sample outgas for a while (up to 24 hours) before taking a kH reading.
72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias
2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.