1) eth price tanked
2) gas prices mooned
3) liquidation auction bots who bid DAI (to burn) to get ETH from underwater CDPs stopped working, due to some combination of running out of DAI liquidity (likely), not being properly configured to participate in gas price auctions (likely), or miner censorship (unlikely, but yet to be determined from mempool data)
4) a single liquidation auction bot was able to bid negligible (near 0) DAI for ETH collateral, they have effectively stolen $4M in sum from the MakerDAO protocol, because the protocol was expecting 4M DAI in exchange for the ETH that was auctioned during liquidation, but it was never received (the CDP holders who were liquidated should have also received some ETH back, but in effect their liquidation penatly was around 50% (more than the 13% it is normally) and they are now owed ETH by the Maker Foundation and will likely get refunded
5) in 48 hours, unless *something happens*, Maker will proceed into *debt auctions* which will inflate the MKR supply and continue to auction until 4M DAI is bought and burned