Perhaps try to have them hard refresh their page - that should do the trick
• Chrome, Firefox, or Edge for Windows: Press Ctrl+F5 (If that doesn’t work, try Shift+F5 or Ctrl+Shift+R).
• Chrome or Firefox for Mac: Press Shift+Command+R.
• Safari for Mac: There is no simple keyboard shortcut to force a hard refresh. Instead, press Command+Option+E to empty the cache, then hold down Shift and click Reload in the toolbar.