Fix Themify Corporate Issues

My client has a Wordpress website which uses Themify Corporate. There are x2 issues 1. Is it very slow. It takes ages for the backend or the website to load. I need to know if this is an issue with the hosting provider, or an issue with the theme itself? 2. The website keeps on breaking and I have to go in to wp-admin and do updates. The main issue is the backround image carousel on the homepage goes blank and the revolving testimonials underneath this stop working. I have had to do this 3 times now to fix it. However, the last time, although this has fixed the desktop version, the mobile version is still showing blank at the top and the testimonials don't work. I need someone to get the website working extra fast and fix this issues, whether it means using new plugins, or editing existing plugins and theme code. If it is the hosting provider, then I need to know how you know this is true, so I can tell my client and discuss maybe moving the website to another server. You MUST be an expert at Themify Corporate I do not want any time wasters or I WILL leave bad feedback no matter how much you beg me not to. So please only professional, experienced Themify developers only to fix this issue quickly.