To his relief, when he opened Illustrator again, it worked smoothly. He was able to work on his designs without any issues, and he was grateful to Rachel for suggesting the solution.
Before applying this specific security hotfix, users must first update their installation to the latest version (e.g., 16.0.3 for non-subscription Windows users). Adobe Help Center Installation & Update Guide Updates for CS6 - Adobe Community 12 Jan 2019 — adobe illustrator cs6 1600 3264 bit updated patch