Header image on my Lucida Pro website sometimes disappears

Hi, I've been using Lucida Pro for about 4 years now and absolutely love it. But on one of my LP sites at www.biha.org.uk the big full-width "header banner" image will regularly disappear about once or twice per week (on all browsers including mobile) and I will need to manually log into the site and re-insert the header banner. I don't have any problems with any of my other LP sites that are hosted with different hosting companies - it's just the hosting company that hosts my BIHA site. I have raised a support ticket with this hosting company, but they are denying any problem and effectively telling me that it could be a problem with the LP theme. However, I know it's NOT a problem with the LP theme because I don't have any problems with the "header banner" on LP with my other websites hosted with different companies. (I can't change hosts for the BIHA site because there are literally hundreds of pages and it has a high Domain Rating (DR) of 62 (Ahrefs) and I can't take a risk of losing any pages or DR. So I'm stuck! Any help or suggestions would be very gratefully received. Thanking you. Mark J. BIHA Founder.