Home formatting issue after latest update

For the mime type error… that is something at the server level.
Perhaps your CSS is not found, but instead of returning a 404 it gives you an error 200 and shows an HTML page (such as your error page).

As for the 404 error and for the uploads/fvm directory being empty, there are possibly 2 reasons:

a) FVM gets the permissions and ownership from wp-content/uploads directory.

Ensure that wp-content/uploads has writing permissions and it’s owned by the server.
You can try to chmod it 777 and purge FVM caches to see if it works.

b) Perhaps permissions are correct, but files are not being generated due to page cache.

If the HTML page is cached (as how it seems it is), but you have updated a plugin or purged the cache, the FVM cache will be empty.
If the HTML page is still cached, it will point to those js and css files which have just been deleted, hence you got a 404.
Likewise, since you are seeing a cached page, FVM won’t be able to regenerate those files because when cache is enabled, PHP (the processing engine) is not running during the pageview and therefore nothing is running other than the html page from cache.

The solution, is to make sure the cache is purged, either with some cache plugin you use or perhaps, on your hosting company control panel.

You can make sure that cache is purged, if you disable FVM on wp-admin.

Once FVM is disabled, there must be no references to fvm generated css or js files on the frontend, and neither 404 or mimetype messages for those files can exist, because if FVM is disabled, references to those files cannot be on the html (unless you are seeing a cache version).

Also try to purge your cache on your own browser.

If anything else, let me know and I’ll reopen the topic.

Ok, thank you!
I cleared cache on Sucuri, that was the issue.

If you cache your site on sucuri, I suggest enabling the option to preserve the cache files on FVM.

That will prevent future 404 when you update something or purge FVM cache and the page is still cached on sucuri.