Seems to me, you have a conflict with some 3d part plugin you have activated.
To find out if this is the case, deactivate all active plugins. If after that customizer works, activate plugins one by one, until the problem occurs again, so you can exactly know what plugin is problematic. then keep it deactivated or substitute it.
If this solution didn’t work for you, post us in private reply your site address and login information, so we can check what going on.