On playground.wordpress.net, if you happen to specify a plugin slug that doesn't exist in the WordPress Plugin directory, it will only install the plugins until it encounters the first inexistant. In the progress screen you can see that theoretically it dowloads them all but then on the Plugins page you can only see the first plugins.

Example: https://playground.wordpress.net/?plugin=activitypub&plugin=inexistant&plugin=biscotti will give you these installed plugins:

If I omit the inexistant plugin it works: https://playground.wordpress.net/?plugin=activitypub&plugin=biscotti

I came to this through the following snippet which, when executed on /wp-admin/plugins.php will give you a Playground URL for all of your plugins:

'https://playground.wordpress.net/?plugin='+Array.from(document.querySelectorAll('table.plugins tr.active')).map(tr => tr.dataset.slug).join('&plugin=')

But if you have custom or premium plugins, it will trip up the Playground.