Hi Ton
In Storefront 16.7, we now support Bootstrap 4 and 3.
The legacy Bootstrap 3 includes Glyphicons, which is a set of 250 icons. But this has been removed in Bootstrap 4 usually in favor of FontAwesome, which is a larger set of around 1600 icons.
Your theme happens to have both Glyphicons and FontAwesome so they are fighting with each other over which icons to show. The easiest thing to do is see if you have a newer version of your theme that supports Bootstrap 4 with FontAwesome. If not, you can post back here and we can help you find another solution (e.g. removing the reference to Glyphicons or FontAwesome).
Thanks