I need help diagnosing a sibilant problem on vinyl

Not enough VTF (tracking force) and/or too much/not enough anti skate could be the culprit. Do you have a VTF gauge?

There many possible causes, including but not limited to:
- inadequate VTF
- sub-optimal anti-bias adjustment
- sub-optimal zenith alignment
- sub-optimal SRA (VTA) adjustment
- overload or shearing distortions in the phono stage
- dirty or damaged records
- inability of the Elys to accurately trace/reproduce HFs
- vibrations at certain frequencies exciting resonances in the cartridge body, tonearm or other components

Searches within the Analog Forum for "sibilant", "sibilants" and "sibilance" turn up 17, 6 and 66 threads respectively. There's already a wealth of information/opinion out there. Any one of the hundreds of posts on those threads might (or might not) provide a solution to your problem.

Truth be told, reproducing sibilants cleanly, especially on inner grooves, is one of the most difficult challenges for a vinyl setup. I have a few especially challenging LPs that bring virtually any analog rig to its knees (and send people screaming from the room with hands over their ears). I've only heard these LPs reproduced cleanly a few times. It can be done, but not easily or cheaply.

Improper alignment.