FanDuel same game parlay rejected after one leg already started

Had this happen last night with a same game parlay for a baseball game. Placed the bet about 5 minutes before the first pitch, but apparently one of the legs runs in first inning was already locked by the time I got to confirm. The system let me set it all up, but as soon as I hit submit it got instantly rejected, even though the other two legs were still open. No error or warning, just booted. Super frustrating when you’re trying to catch the edge right before the odds shift.

Not the first time either - slots and promos usually don’t glitch like this for me, but these parlay things seem way more finicky. Anyone else getting this? Is there any way to tell which legs are about to lock before you go through the whole setup, or is it just random timing and luck?