Theme Customizer Not Working

Hi There Since the last Wordpress update on Friday the theme customizer is not working on Clean Education Pro. I have already tried deactivating and reactivating my plugins one by one - but this didn't work. I also contacted my host to confirm they were running the right php version (which they are). They also couldn't find anything on their side to be causing this. I then deleted and replaced the Clean Education Pro theme and made sure it is the latest version - but this did not work. When I try another theme such as the default Wordpress ones - then I can use the customizer normally. So this does seem to be a problem with the theme. Pleaser advise asap. Kind regards Loz