Polymarket halted trading on its prediction-market order book for four hours and 17 minutes on Monday after a delayed open-order read failure recurred about five hours after an earlier outage was marked resolved. The first incident began at 00:40 UTC as a major outage on the Trading API and prediction markets; the platform entered cancel-only mode at 01:06 and closed the event at 01:12 after 32 minutes. A second incident opened at 06:23 UTC, escalated into a trading pause at 06:30, and was marked resolved at 10:47 UTC after resumption targets slipped from 10:00 to 11:00 UTC and a brief cancel-only window. Both events shared the same status description of delayed open order read responses. The disruption was limited to the order book: the web app, account access, websockets, market and position data, Polygon on-chain settlement, and perpetual products stayed up. The affected stack is Polymarket’s CLOB v2, launched April 28 with new exchange contracts, a rewritten backend, and pUSD collateral. Polymarket has not published a root cause, confirmed whether orders or resolutions were affected, or addressed compensation; The Crypto Times has sought comment.