Subgroup expandy triangle turns into unknown icon when clicked
On the Contacts - Manage Groups page, if you have subgroups and you click the triangle to expand to see the subgroups, the icon becomes an unknown icon.
AFTER CLICKING:
It's coming from civicrm.css and was part of https://github.com/civicrm/civicrm-core/pull/17296.
I think it's missing font-family: "FontAwesome";