Many workplaces use a corporate firewall, and on the admin panel, they can enable-disable categories of websites, like "Porn", "Adult themes", "Gambling", "Social", "Video streaming", "AI", etc. One of the categories could be "VPN", *.mullvad.net can fall into it, and it could be that they disabled that category. At many workplaces, it's against the rules to circumvent the company's monitoring, and so, many of such technologies are banned.
I don't think that .ai is automatically filtered in this case, it's more of a case by case basis. But it's killer nevertheless. "Adult themes" for example is a large umbrella at OpenDNS, and for example I wanted to check the lyrics of a song I was listening to, and it was hosted on darklyrics.com. Nope, couldn't visit, because it's Adult Themes.
