Check if you have correctly connected fonts and icons in your project. SuiteCRM documentation says that to display icons correctly, you need to make sure that all font files (e.g. woff, ttf) are in your project folder and correctly specified in the CSS file. Check the path to the font files and make sure they are loaded correctly (Loading new font types to SuiteCRM).
If the icons still don’t display, there may be a problem with your browser cache. Try clearing the cache or open the page in incognito mode to see if the icons have been updated.