The aquatic form dredge is not putting the card at the top of my deck multiple times today. I did not have the mana to draw it and I did no follow up to alter my deck following. I dredge for cultivation (8 mana) on turn 6 and I did not draw it next turn.
Your opponent played some effect that shuffled your deck.
Likely a DK with a Plague card, but there are other ways also.
I just had the same problem. There was no deck manipulation from the opponent. No shuffle, no discover, no plague, no mill, no draw.
It was just a regular turn where they played a minion with no discover or deck manipulation. I’ve had it 3 times today now.
I just had it happen to me twice with no deck manipulation or shuffling into my deck. Just a regular turn where they played on minion with no shuffle, burn, discover, plague, or draw effects.
Did your opponent attack you with a Staff of the Primus?
Do you have a game replay recording available? Without that, there’s no practical way to investigate.