When using Elastique-Soloist-Monophonic, esses are sometimes scrambled.
This have been an issue for a long time actually. Here are mp3s with Reatune On and Off. There is one S in the middle and the distortion is clearly audible.
https://drive.google.com/file/d/1Z6a...ew?usp=sharing
https://drive.google.com/file/d/1bmj...ew?usp=sharing
If this is an issue with the Elastique algo itself, then the possible solution could be to implement an S-detection and do no process esses.