I've just got that message now on Hekaton Prime with SC 13 in inventory. It's correct.
Here's how "one member X% chance" works. When the boss dies, it picks one person with the quest Enhance your weapon from the killing party. Everyone else is out of the loop since that point. If that person has 1 SC of stage within the specified range, RNG decides whether he/she gets a higher stage SC or message 975 The soul crystal was not able to absorb a soul. Otherwise something is wrong, and he/she gets one of:
1265 You can't absorb souls without a soul stone. --- no SC in inventory