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I believe that the issue might be related to the GPU as you're seeing artifacts and flashes when you try to hold down shift while scaling.
I would recommend updating the operating system and see if it helps.
Also, you may try the steps here: Troubleshoot Photoshop graphics processor (GPU) and graphics driver issues
Thankyou Sahil for your reply. Our IT dept wil not allow OS update, and woudl prfere nto to becasue of the issues in link below and time consuming to roll back.
I did not restart my computer, so your link was helpful as I thought I disabled GPU but did not restart app. Will retry later as have a hot deadline and multiple images in progress.