@ajd5 It’s actually due to the rollover adjustment. You initially bought the Brent May contract which expired about 30 minutes ago. However, in order not to close any existing positions, we automatically roll them over to the next futures contract → Brent June, that happened an hour ago.
However, as futures contracts might slightly differ in price, an adjustment needs to be made to keep the rollover neutral. For example, in your case, since you’ve bought Oil & the next contract is $1.5 higher, an adjustment of [quantity x $1.5] needs to be made in order to neutralize the difference. For you, the current adjustment was negative, however, if you were short, the adjustment would’ve been positive. The end result is always the same - keep the position profit/loss as if the rollover never happened.
Have you not received any notifications today warning you of the upcoming rollover?
There are plenty of discussion around this topic if you wish to learn more: