This might be relating to the merchant code use by the site/venue… A lot of the newer online venue are based out of Cyprus gambling licences and are not “playing fair” with the card transaction type, and often using multiple merchant names to get around blocks/anti-fraud checks.
Have you previously had transactions blocked for this site via starling, or was it a new sign up to a site?
Uniquin ltd / Inet1 are one of these type of merchants not using correct code formats.
Would highly recommend you sign up to https://www.gamstop.co.uk/ they are proactively distributing a database to all gambling sites online to make sure any new places continue to block existing users who identify as having a problem
Although I’ve noticed that Revolut only apply block settings for online transactions etc to set cards and number, so may well be card settings.