Wordpress site problem - site not loading properly

I have a Wordpress website that has worked fine for years, I update plugins regularly. Unfortunately a couple of weeks ago, it stopped loading properly; sometimes pages load okay, sometimes not. I had the host move the site to another cpanel server, which has speeded the site up but, it still has a problem rendering the images and loading properly. We use Sucuri and they've checked for Malware, but they say there isn't any. Need an expert to take a look.