Ok, then it may be a cache issue. I spoke to someone from my hosting company SiteGround some hours ago after you first mentioned that I should try to clear or temporarily uninstall all cache plugins and test how it works. The developer always told me that the option to disable it through the SiteGround plugin was not there. That’s why I told SiteGround to turn it off through their end. I will have a meeting with the developer in a few hours, so I will forward over the the instructions the hosting company gave me turn it off through their plugin on the backend if it’s still on. And if it is turned off from the backend and there are no other caching plugins, apart from the Optimizer (SiteGround plugin), it would mean the problem with the appearance is not related to the cache.

I was also told that the issue might have happen if the website is using WebP copies of the images for example ( there are some browsers such as Safari that do not yet support WebP). I then told the rep that I was using Smush plugin to compress and optimize the images on the site, but I disabled it recently. Then rep stated that even if I disabled the plugin (Smush), that usually when the images were compressed, even if the plugin is no longer active the images are loading from the compressed format.