I’m a broadband tech for a large media company and we visit alot of people who are having similar problems with their Internet.
We can rule out that you may or may not be between to acess points (router and boosters) and your devices are jumping between them as you’ve already mentioned your computer is hardwirded.
Have you tried looking for any sort of age restriction setting in your providers companion app, I know when our age restrictions are on with it set to age 13 as a default setting as a new customer it can cause issues like emails not displaying attachments fully as it thinks the attachment is a virus, Netflix buffering if your trying to watch Peaky Blinders for example which is definitely an 18 rated show and any type of adult sites like mucky sites or in your case gambling sites would be displaying the circle of doom (buffering). All you would need to do is change it to either the 18 plus setting or disable it all together.
I hope this helps, it might be worth checking your providers companion app or calling your provider, you never know and if this does fix your issues then I would like one bonus on Vampy dedicated to me, ha ha, I dont mean I want the winning, I would just like to see what it would be worth.
Good luck.