The History panel within Photoshop is something most users have made us of in their workflows. One of the most common things I see happen with beginners is accidentally erasing History Steps (aka History States). This generally happens when someone clicks a Snapshot not realizing that can erase History, or more often someone chooses a previous step and does something new. If you add non-linear history to your workflow that's a quick way to keep as much of your history as you've set in your preferences. Enjoy!
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