Sorry to hear about this issue. Have you tried the plugin deactivation route, i.e., deactivating all of the plugins except BB then see if the problem is still there. If the problem is gone, reactivate the plugins one by one until the problem reoccurs to find the 3rd party plugin causing the issue. If the problem still occurs after deactivating all the plugins, we might need temporary admin access to the site to dig in further.
I’ve restored the page to an earlier revision and is now editable. Maybe you can have your client reinsert the slider and see if the same problem happens? I tried creating a test page and inserted a content slider and a slideshow and it works fine. If possible, try to ask what slider module is used, as well as what images, properties, etc. Or if another slider is used since I can see 2 other slider plugins installed.