Hi, thanks for the quick response. Unfortunately the site is running PHP 8.2.23, so upgrading will not help.
Re what we are trying to achieve I cannot answer as the cron job appears to have been created by shortpixel itself. Only comment I can make is that we do have image folders with images that are NOT part of the wordpress media library but cannot see how this would be related to the issue above.
Thanks again for your help.