Has version 3.0.9 been tested with Wordpress 4.9.8?
I don't want to upgrade my version of Wordpress if it is going to break.
Sure, let me help you with that.
So far we know that the latest Version of S3, which is 3.0.11 (single) and 3.0.12 (studio)
works with WordPress 4.9.8 (but please do not install Gutenberg).
So I personally recommend you to update your Semplice to the latest version,
and then update WordPress.
Before you do, please do make a backup just to be sure.
Let me know if that helps