New install on a new (well second-hand) iMac and Bridge looks to be having a fisty-cuffs with the graphics card. Have tried changing the settings in Bridge and Camera Raw setting to enable/disable hardware acceleration etc but to no avail.
Well the first thing I'd do is to update your Bridge and Adobe Camera Raw. I'm seeing ACR v. 12 and the current release is 13.4.
Try updating your software from the ACC app and please let us know if this solved the problem.
Well that solved that! Thank you Gary! I had just installed everything direct from ACC app, so wouldn't have conceived I'd need to update anything manually!