During Girgashiy raid (preferably normal difficuilty), soul absorption can be interrupted if sufficient damage is dealt during casting phase. I.e., purple bar will show up for ~6 seconds, but Girgashiy can be attacked during last two seconds.
A well-timed meteor strike, judgement blade (with crit), or few people using final hits during last two seconds should be enough.
If soul absorption is interrupted, harmless souls will be summoned regardlessly and they will still run towards Girgashiy, but they will not do anything, as the purple bar already disappeared.
In a party of 16, it is possible to have 16 souls getting stuck, making them perfect targets for many skill and subskill training (just don't use hydra). Although, it is strongly recommended to tell your party you are doing it, or people will end up attacking the fake souls and getting themselves killed because Girgashiy will use soul absorption again.
Also, when souls are about to come out, quitting the raid can actually bring those souls outside, and you can see headless skeletons with names "human", "elf
or "giant", which is kinda creepy.