When things go a little crazy and people are asking why icons are missing or why a theme change hasn’t come through, this could be a sign to clear the Moodle Cache.
This is not the Browser Cache which can be cleared by various means in each browser. See https://www.refreshyourcache.com/en/home/
There are two types of cache. Moodle has its own internal cache which impacts everyone, so clearing this cache can be completed using the admin function ‘Purge Cache’. The other type of cache is a browser cache. This can be cleared by the user in their browser. Don’t get them confused as one affects each individual user and the other affects the content delivered by Moodle.
Site administration > development > Purge Caches