A UKGC licence is the baseline, not a guarantee of a smooth experience. Check...

https://weekly-wiki.win/index.php/What_Are_Red_Flags_for_RTP_Transparency_on_a_Slot_Site%3F

A UKGC licence is the baseline, not a guarantee of a smooth experience. Check that RTP information is easy to find, withdrawals are processed promptly, and responsible gambling tools are simple to use