If it says, "Processing..." then you have some AudioSnap edited tracks or some other changes to a track that must be processed before the Mixdown can begin. I went through that a few times where an Export took 8 hours because of that in X1a. After X1d went away this was less of an issue, but you may start looking at "Bounce to clips" in any audio tracks you alter via AudioSnap, for example. Keep a backup of the original track audio, and I've begun validating where the bounced clip is stored, but this is likely why it's giving you those several times (one per track).