When I browse through my Blueprints folders, the content browser somehow collects child actors from other Blueprints and starts displaying them in other Blueprints that have nothing to do with it.
Some of these child actors have particle effects in them etc, so the performance of the content browser completely tanks while it tries to show child actors in other BPs as well. With high amounts of child actors inside BPs, the content browser completely destroys every performance of the editor, making it unusable as long as the content folder tries to show any BP previews.
See screenshot (child actor is candle BP with particle effects, which is shown in Content Browser preview of doorframe BP (left). However, it does not exist in the doorframe BPs (right)).
