Sugar Professional edition international access?

Help please — full disclosure, I have no background in IT, Computer Science, Networking or Programming. I was superficially assigned as our SugarCRM Professional edition administrator at my company in 2017 and am self-taught in managing our business needs in Studio. I oversee a team of roughly 40 Sales people domestic (US) and 1 salesperson located in Scotland who supports the UK/EU. Here in lies the trouble — our International sales person claims he cannot and has never been able to access our instance of Sugar via the URL while abroad. I have not been able to get a straight answer from Customer Service on why that is (is there a .uk or .eu version of our Instance URL that exists that I am not aware of that is needed to access in these countries?) and now we are onboarding an Australian sales rep and I have no idea if or how he will access the system in his territory. I talked to our internal IT guy about this already and he suggested the loading speeds may be just so slow that trying to login they're being throttled, rendering the instance "accessible" but unusable, but I have no sure way of knowing that this is the issue. I've scoured the internet and forums but can't find anything that addresses this particular concern and customer service / support has not provided solutions. Any advice would be greatly appreciated, thank you.