Another here with a transfer rejected by Qatar. Going into the My Redemptions section of MR, and manually searching for dates that include today (as today isn't visible automatically, for some reason), shows the status of the redemption is "TI22" where it would normally say "Completed".
Online chat confirms transfer rejected by partner and they've offered to investigate (and hopefully, resolve, honouring the current 2:1 redemption rate). I asked if they could just give the Amex points back immediately so that I could transfer to BA instead (to get them as Avios in one way or another), but they said they have to raise the ticket anyway, so I suggested sorting the transfer to Qatar would be best if they can.
Long story short, maybe try sending your points to BA, while the rate is still 2:1 online! I'd made a couple of other transfers to Qatar this week from the same account (one bulk transfer before I forgot, and another smaller transfer over the weekend when extra points posted), so I guess the system doesn't like that many inbound transfers in a short period.