Everyone who uses Cleanshot has that problem. No many replies from the manufacturer either. Cleanshot attacks brass/copper. The cases should be cleaned in NON-ammonia [ammonia attacks copper also]cleaner as soon as possible [the vinegar based windex is good], wiped clean inside and out, dried, and then tumbled. A small soft nylon bottle brush cleans the inside of the cases. Many will still turn dark but you can stop the weakening process indicated by the green oxidation.
Hope that helps. Cleanshot works very well in the larger cases such as 45-70.