https://github.com/pichalite/nodebb-theme-slick/issues/60

public/src/client/account/settings.js

@@ -8,7 +8,7 @@ define('forum/account/settings', [
 
 	// If page skin is changed but not saved, switch the skin back
 	$(window).on('action:ajaxify.start', function () {
-		if (ajaxify.data.template.name === 'account/settings' && $('#bootswatchSkin').val() !== config.bootswatchSkin) {
+		if (ajaxify.data.template.name === 'account/settings' && $('#bootswatchSkin').length && $('#bootswatchSkin').val() !== config.bootswatchSkin) {
 			reskin(config.bootswatchSkin);
 		}
 	});