Welcome to GPLDL - we are still beta - please report any bugs via the contact form.
Working solution for Yoast SEO Premium version 9.5 (any maybe following):
To remove the annoying notice “You have not activated your Yoast SEO Premium subscription yet! This Means you are missing out on features you for a paid, SO the activate your subscription now!” in the composing post/product page do the following:
in the file wp-content / plugins / wordpress-seo-premium / premium / assets / js / dist / wp-seo-premium-metabox-950.min.js
find
if(403===e.status
and change to
if(403!=e.status
Save the file and reload the page (delete browser cache before)!
Et voilá: No more nagging notice!