The styles are not loading, because, you have purged the css/js files but not your server page cache, or some other page cache plugin.
The pages are pointing to minified css files that you have deleted, either on purpose or not, it doesn’t matter.
Another possibility, is that the server has no file permissions to allow saving those files.
All you need to do is to disable the plugin and then clear the page cache.
Look for any other cache plugins you may have installed and purge everything.
Then ask your hosting to purge their own cache (check their control panel).
If you are using cloudflare as well, depending on the features you use (such as APO) it may be cached there as well.
Some hosting services have very persistent caching, so speed optimization that requires minification of css and js files, it’s best done by a professional (or get a better server provider, ie cloudways for example).
FVM has an option to preserve css and js files instead of deleting them immediately when you clear the cache. It will keep the files for some time, to prevent accidents where your page is still cached but you already deleted the optimized files (the filenames change every time you purge, that is why you cannot load them as your page is still pointing to the old ones in it’s cache).
FVM does not do page caching.
For your type of cache, make sure the “Purge Minified CSS/JS files instantly” is not active.
But first you need to configure it properly, which may prove difficult as your page cache is apparently not updating when needed. Basically, every time you change something on the site, the cache should be purged.
If your hosting cannot sort it out, follow the instructions I provided here.
Emergency fix is to deactivate the plugin, followed by page cache purging.
If you used some cache plugin and disabled it after, you may still be having cache rules on your .htaccess file.
Check the site files (control panel, plugin, sftp, etc) and delete the wp-content/cache directory manually, if it exists.
