Debit cards are not stable in many companies due to reasons behind the VISA and its sister companies. Wirex cards are only one that works flawless as far as i know from the feedback of other users. Is situation same with your cards?
But have you had problems with VISA in the past? You could have the same problems with Wirex if they decide to block your card or a transaction or want authorization before they send the debit, although that can be considered a security feature which these cards should have for larger amounts.