MMs are having trouble modeling these negative strikes. For many of them there are only low ball bids, and a few egregiously high offers. Switching from a lognormal to now normal distribution model is a big game changer for everyone. Everyone's hedge ratio has been completely altered as the WTI Jun20 (0) strike put's delta goes from close to zero to, to somewhere between 10 and 15.
When the front month dips below zero you have to trade WTI options like an F/X pair or options on a listed spread (e.g WTI-Brent, Soybean calendar spread options CSOs) which theoretically have unlimted upside and downside moves in the underlying. Traders and market makers are having trouble adjusting to this concept.