Can you please give an example of the sites that are not working ? What browser do you use? What operating system do you have? What happens if you go to https://phishing.threatops.co.uk (safe testing site) ? Is the behavior similar to the behavior when you visit sites you are referring to?

I primarily use the current version of Edge browser on Windows 10. The issue I'm facing seems to be affecting various sites, including those with dynamic content like video streaming platforms and interactive web applications. When I visit the safe testing site you mentioned (https://phishing.threatops.co.uk), the behavior is quite different compared to the problematic sites. The safe testing site loads quickly, and all elements seem to function properly. I've tried clearing my browser cache and cookies to see if that might help, but the issue persists. Any Suggestions? epayslips, Expert HR Services, competitive wages  nexus.iceland.co.uk

@Andrea-Smith I still do no see examples of problematic site URLs. Could you maybe provide some screenshots how the sites look like on your computer? Is the behaviour same in all browsers? 

There's very little extra information, but for future readers: if there's an issue on Google Chrome browsers accessing Microsoft and Google websites (but other websites load fine) you may have the same problem we had.

It turned out that content restriction profiles (either via a config profile or via Screen Time > parental control, e.g. if it was synced via a personal iCloud account) mess with Jamf Safe Internet being able to access these websites. If you turn off the content restrictions, JSI works fine.