Not able to add featured images on subsites

I have your plugin on a dev site where my client wants the shared media library. They also want some post types on the primary domain and some post types on the sub sites. However, I am running into an issue where I cannot upload a featured image on any sub site post types.

I have disabled all other plugins, and turned on debug and cannot find a solution. The only way to get featured images to save and stay attached to the post is to disable your plugin.

Can you help?

Start by reproducing the featured-image upload and save behavior for post types on a subsite with the Network Media Library plugin enabled, then compare it with the plugin disabled while reviewing WordPress debug output. Trace where the plugin handles shared media and subsite posts; done means featured images remain attached to subsite posts without disabling the plugin.

Written by the indexing model from the issue text.