Unexpected error while working with grouplayers in Geoserver 2.26.0

Hi, Im have previously updated my geoserver to 2.26.0
I was working on it and manage some raster data tif, group some of them successfully via grouplayers and created a well working WMS to include it in QGIS.
Now while everything works fine, promplty the geoserver interface shows an error “Sorry, an unexpected error occurred while processing the request on the server.” this just pop up when I choose the grouplayer, which means I cant continue with working here.
Does anyone has the same problem and probably a solution for me.

Thank you