S3 is Krakli's String machine plugin and if I am being honest one of my personal favourites. The Mixfilla patch has been used in more of my tunes than I can care to guess.
Again it is one of the older Krakli plugins and as such falls foul of the multi-core bug. If you do want to use more than one instance in your compositions a work-around is to copy the S3.dll and rename it to S3_1.dll, S3_2.dll etc. These new instances should then be available to select in your DAW.