Any 8 speed Shimano or SRAM compatible cassette will work. The cassette is not to blame for your shifting issues, unless you have something other than an 8 speed cassette. The CS-HG50 designation was used for cassettes from 6 speed to 10 speed, so that doesn't tell us much without knowing how many cogs are on it.
What rear derailleur is paired with that shifter? You could have a derailleur that is not compatible or you could have the cable routed incorrectly on the derailleur. On some of those derailleurs, routing the cable on the wrong side of the pinch bolt changes the pull ratio.