I've seen the quality control thing thrown around on here, so there may be separate instances of "on hold," and this may or may not apply to yours - so take it with a grain of salt. (disclaimer)
It sounds like orders just came pouring in, and with the new allocation rules (each order counting against a future allocation), some dealers went WAY over. They have a lot of cars ordered - but no available allocation to "earn" them. If I understand correctly, all orders that went over the allowed allocation have been put "on hold" and will remain there until the next allocation, when the dealer gets more earned slots to match them with. I don't know if this is something they're starting effective now or retroactively, and again, there could be other reasons to have an order "on hold," so take it with a grain of salt.