OBS comes with a very small offering of automation: change scenes when a specific app is in focus. The idea seems to be to follow a tutorial or a multi-game session or something like that, while you just "do it". You set that up in Tools -> Automatic Scene Switcher.
Did you perhaps play with that, and forget it was there? Your description sounds exactly like what it does.
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Note:
The native "Automatic Scene Switcher" should not be confused with the "Advanced Scene Switcher" plugin that grew out of it and has taken on a life of its own. It completely covers the native functionality and a TON more!
This plugin will allow you to automate various tasks using "Macros". Macros consist of a list of conditions under which a list of actions will be performed. Examples and guides can be found in the wiki. Feel free to contribute! If you run...
obsproject.com