Check to see that you have the latest or last released KAT500 Utility.  The current KAT500 firmware version is 1.75.

Based on your description of the activity, it would appear you are operating in the AUTO mode.   I suggest you set to MAN mode, select the antenna of your choice and frequency desired, and press TUNE on the K3S, and then TUNE on the KAT500.  This will resolve a match and store the data.  I've done this for all antennas and the frequency ranges I use.  Thus I've "trained" the KAT500.   When I change my K3S frequency/band, the tuner follows and selects the pre-stored values for the match.  

With my 3 antennas, I can operate 160M - 6M, any frequency on those bands with a 1.5:1 or better match.  

73
Bob, K4TAX