Are all users(including you) using the same exact browser and all fully updated? Don't assume, I know lots of people that prefer Edge or Firefox over others. For example at my office most of us use Chrome because we use some extensions that are not available in other browsers. We still get users that use Edge and Firefox for their daily tasks and just switch to Chrome to use the extension or whatever.
If the users are working from home do they have a company provided computer that has decent specs or are they on their own computer that may be a little older? I know it is in the cloud but this does still matter when loading some stuff. I've got great internet at home but have noticed some things are a little less responsive for me as well. I'm not sure of the exact cause but it may be because I have a lot more going on on my home pc than I do at work. Specifically many many more extensions installed in my browser.
I would have them try a fresh browser and see if the issue persist. If they normally use Chrome have them install and try Firefox. If the slow loading continues then the issue is not the browser or their extensions.