KH values went up by a notch

Have been using the kh director for nearly a month. I struggled to tune in initially but eventually was able to successfully configure it. I recently received the kh reference solution and it shows 7.7 which is off by .2 which I am ok to live with. This was just two days ago. Now suddenly the values went up by .7 for no apparent reason. What could be the reason and how can I troubleshoot this?

Did the readings of the tank water or reference went up? And is this increase constant?

The difference used to be .1 but within a day the kh director reads .7 more than Hanna which I am using as a reference.

If the increase is constant, check if the calibrations are still correct and/or check what the KHD measures when using the reference solution.