They make the case that May was a positive month for US equities, hence rebalancing flows will result in outflows for the dollar. This matches up with what Barclays argued from last week here.
At the same time, Deutsche says that their model also points to positive flows in the CAD and GBP. This comes as both Canadian and UK equities have lagged behind their US counterparts this month. In that lieu, they see the most selling in USD/CAD and most demand in GBP/USD for this month-end.
Typically, these flows can play out during the week but they can be particularly evident at the London fix in the last few days of the month. So, that might be one to watch out for later today or tomorrow.