Does this happen to all pages or tabs or just some of them?
If you use another admin account, would the issue persist?
And if possible, please also try switching to another network and see if the issue persists.
Besides, I would suggest first having a check in Microsoft 365 admin center>Service Health to see if there are issues which may be related.
If there aren't any, since the cause of this issue may probably due to backend, please consider involving support for help via Microsoft 365 admin center>Support>New service request.
Thanks for your understanding.
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