If I had to guess this is fall out from the rate increase Visa put in place after Brexit. Now that they are no longer restricted by pro-consumer caps they hiked the rates from 0.3% to 1.5% on credit card payments: https://www.ft.com/content/4820b619-4d35-4c6a-8523-fc685c047...
That's only for cross-border transactions between the EU and UK, and as the article says Mastercard is doing the same thing as well. I know there was a lot of speculation on social media that this was to blame but there's a lot of social media misinformation whenever someone finds a way to blame anything on Brexit... (Also, in practice people were getting ripped off by banks on the exchange rates for those cross-border transactiopns anyway. A lot of these EU measures require being part of the Euro to get the full benefit, and the UK isn't because we'd likely have gone the way of Italy and Greece if we joined.)