Some missions have been changed in significant ways. Some have changed to outdoor missions as you suggested, and others have had bug fixes applied.
When this happens, you may be offered the mission again. It's up to you whether you want to play the mission again. You are free to do so, or ignore it the second time.
This is how adjustments to content will continue to be phased into the game. We want to give you the maximum flexibility to enjoy the new content.