Hello @cegasol,
The SiteGround Optimizer plugin relies on the following WordPress cron tasks to generate WebP copies or optimize the images:
siteground_optimizer_start_webp_conversion_cron
siteground_optimizer_start_image_optimization_cron
However, the WordPress cron system is disabled by default on the SiteGround Staging environment. This is done in order to prevent the staging sites from executing tasks related to WooCommerce orders, sending newsletter emails, etc.
That being said, when the WordPress cron feature is disabled, SiteGround Optimizer would not be able to schedule and run those tasks.
Please, try to optimize the images on the main site instead.
If the issue persists, do not hesitate to contact us from your SiteGround user area so we can review the issue in detail.
Best Regards,
Daniela Ivanova