Fonts/CSS are not loaded

I’m using a WordPress site hosted on SiteGround with SiteGround Speed ​​Optimizer and SiteGround CDN (Premium) enabled. On some office PCs the site loads occasionally wrong text colors and missing CSS/font style: for example text that should be black appears gray during normal browsing, while the same page looks correct incognito. A difficult to reload (Cmd+Shift+R) fixes it immediately.

What I captured (Chrome DevTools → Network → the CSS file) Here is a screenshot of the response headers for a CSS item when the page looks wrong:

• Cache-Control: max-age=31536000
• Expires: Wed, 10 Feb 2027 ... (1 year)
• Content-Type: text/css
• ETag: W/"6989fce4-4429"
• Last-Modified: Mon, 09 Feb 2026 ...
• X-Proxy-Cache: HIT
• X-Sg-Cdn: 1

So this CSS can be cached explicitly 1 yearand it is also served from cache via SiteGround CDN/proxy (HIT + CDN enabled). SiteGround’s CDN documentation states that it can origin caching headers such as Cache-Control: max-age / Expires (And max-age=0 means “do not cache”).

My most important question
What’s the right way to prevent users from seeing outdated/mismatched CSS (wrong colors/typography) on WordPress + SiteGround CDN/Speed ​​Optimizer, without asking people to hard refresh or clear the browser cache?

Additional context

• The problem is also visible to logged out users (regular visitors).
• Incognito usually shows the “correct” style, while a normal profile sometimes shows the “wrong” style until a hard reload.
• Mine .htaccess file does not contain explicit mod_expires / ExpiresByType rules for CSS/fonts, so I’m not sure where the max-age=31536000 is set (Speed ​​​​Optimizer, SiteGround server standards or a plugin/theme).