Generally, when the product images on your product pages suddenly disappear, it is the result of a conflict with an app.  It is likely that the app is causing a JavaScript error on your page, which in turn breaks a lot of the other functionality on the product page, including the gallery, variant selections, pricing, inventory, etc.

When this happens, the first thing you should do is disable or remove any new apps you've added recently that might affect the product page in any way.  If that solves the problem and you need to use the app, you will need to contact the support for the app developer for help troubleshooting your issue.

Another common reason for this happening is that an app has been uninstalled recently, but it has left code behind in the template files that is causing problems.  When you uninstall an app, the coding installed by that app is not removed from the theme files automatically.  If you noticed the issues started to happen after uninstalling an app, you should check the app documentation or support page for advice on how to fully uninstall the app.  You may need to reach out to their support team for help with this.

While we always do our best to help our customers troubleshoot issues with third-party apps, these can be very difficult for us to troubleshoot.  We aren't familiar with the coding used in the apps, and the errors produced are often ambiguous in nature.  Your best bet to resolve these issues is by taking a proactive approach in installing apps.  You should always make a backup of your theme before installing any apps that might affect the front-end of your site.