If this plugin is Network Activated only (not per site) the first time, the table "cloud_blocks" is not created when a site is accessed (and this plugin loaded).

WordPress database error Table 'mydbname.myprefix_3_cloud_blocks' doesn't exist for query SELECT * FROM nytt_3_cloud_blocks made by require('wp-blog-header.php')[,...,] WP_Hook->apply_filters, CloudBlocks\Blocks\Blocks->blocks_register_styles, CloudBlocks\Blocks\Options::get_all

This because the custom table creation is only called at plugin activation.

For a plugin, that creates persistent changes like this, to be network (Multisite) ready , it must check that it's installed upon loading (at least admin_init) by an option or directly checking existence of the resource (table). If not, run the installer on that site to create the tables.

Looping through sites at activation is not recommended as it dosn't take are of new sites added later.

I suggest get_option( 'cloud_blocks_installed' ) or similar in this case.