Tested on several multisite networks and if, and only if, network activated it does not load any blocks on admin Cloud Blocks page.

If activated per site it works, so it's not multisite related, but the type of activation. If per site activated first, then network activated later, it stops working, even if site activated on all the sites.

A script is not loaded on the admin page, it seems, but no console errors.

Only difference between network activation and site activation is the order of including the main plugin file, but haven't been able to find the actual reason for this strange behaviour by studying the code.