Multisite setup issue with a sub-directory structure

I’m using the SG Optimizer plugin on a multisite setup with a sub-directory structure. It seems to work fine on the main site, but when I view the Chrome console for site 2 I see a lot of 404 messages for Siteground Optimizer assets due to the wrong path being used.

The assets are being stored in the correct upload directory ( mysite.com/upload/sites/2/siteground-optimizer-assets/my_file.min.js ), but Chrome console is showing the site’s looking for the assets using the sub-directory in the path ( mysite.com/sub-site/upload/sites/2/siteground-optimizer-assets/my_file.min.js ).

SiteGround support told me the plugin is not multisite compatible and I should deactivate it on the sub-sites. However the Purge SG Cache and Heartbeat control seem to work on the sub-site so I’m not sure deactivation is the best solution. How can I fix this?