I encountered this bug on a brand-new baseplate, after importing a few baseparts shown in the video (From an older file). A video demonstrating the issue is attached. Please find detailed system information in the attached DxDiag file.
System information: DxDiag.txt (96.0 KB)
Enabled Beta Features: Aerodynamics, Assistant Preview, Dragger QoL Improvements, EditableImage and EditableMesh, Face Capture, Live Animation Creator, Material Generator, Multilayer Wrap Fix, New Audio API, New Base Materials, New Studio Camera, Scripts Are Non-Strict By Default, Simulation Pause and Stop, Texture Generator, UIListLayout Flex Features, Updated Roblox Controls, Video Uploads.
Restarting your Roblox Studio doesn’t resolve the issue.
When i deselected a part i had previously selected/moved, the ‘blue’ outline would stay. It wasn’t something game breaking, but it was annoying indeed.