With JAI-Ext Enabled:
Go to Settings: Image Processing.
Move Warp operation from JAIExt list to JAI list and submit.
Warping operations will now use standard JAI Warp Operation instead of JAIExt one.
Go back to Settings: Image Processing.
Switch back Warp operation from JAI list to JAIExt list and submit.
It looks like Warping operations are still using standard JAI Warp.
JAIExt enabled: -Dorg.geotools.coverage.jaiext.enabled=true