This has happened to me before (and before v2) but I just got two winning trades in a row taken from me, worth $376 in total. I check Reddit and I see others have reported the same scam (for instance https://www.reddit.com/r/Polymarket/comments/1szg0yt/some_bs/ )
Here's what happened this time: I bought 176 UP shares of Solana 15 min (1777547700) at 30/04/26 13:29:54. The shares enter my account and there's a trade history entry saying I own 176 UP shares. Then the market goes in my favor as it expires and I've won. Except the trade entry for 176 shares just disappears in front of my eyes, and notifications now has a new entry saying "Buy up failed".
Then at 30/04/26 13:34:54, I buy 200 DOWN shares for Bitcoin 5 min (1777548600). Exact same thing happens. I win and then the shares are recalled. Evidence for the purchase disappears except from the Notifications entry and of course my own local data which recorded the buy from the api response.
What the hell? I've endured up to 7.2% fees (thankfully no longer the case) in stride and now hundreds of dollars of wins are taken from me inside of 5 minutes.