It has sometimes bugged out, and refreshing the page tends to fix it. If this doesnt fix it your administators may have change the settings for your Power BI service so I would check with them.
Do you have this issue for app workspace or the new app workspace (Preview) in Power BI Service?
By my tests both of the app workspace, I cannot reproduce your issue.
I am the owner of the workspace, but can't add new members to the workspace.
Could you share some screenshots to specify your scenario?
This is may be a temporary issue.
It seems that you have solved your problem, please always accept the replies making sense as solution to your question so that people who may have the same question can get the solution directly.