Hello ACollingwood,
We understand that few users are getting AADSTS165000 - Invalid request error while accessing Office applications.
And this issue is happening only while using iPads with Smoothwall browser and Google chrome.
You are able to access applications on the same platform and effected users are able to access when they sign-in after your activity.
This happens on iPad browsers as they fail to maintain session cookies during authentication flow. But in your case few users are able to access and issue is only with few users.
And let us know the behavior when the effected user tries to access through Edge browser instead of Safari.
And I request you to exclude the below Microsoft URLs from SmoothWall content filtering.
login.microsoftonline.com
login.live.com
*.office.com
*.microsoft.com
*.sharepoint.com
Please let me now if you have same kind of permissions on the device as other two users. (Do you have administrator permission on the device, and they have only user level permission)