Normally when you finish 1 invasion you wont be able to do the stages again...
BUT, when you fight the last boss in the last stage and you just hit alt+f4 to get a dc and then relogg into the game again, you are able to repeat the Invasion.
you won't get the boxes from stage 2 to 3 or from the last boss but in stage 2 you can farm shards from the mini bosses.