SharePoint Online: Unexpected errors accessing files

We are continuing to work closely with Microsoft to identify the root cause of the intermittent issues you may be experiencing. As the issue has been difficult to reproduce consistently, investigation has taken longer than expected.
A likely underlying cause has now been identified, and more detailed analysis is currently underway.

If you are encountering this issue, you may find success by using a private or incognito session in a web browser.
If this does not work immediately, making several attempts at closing all browser instances and retrying in a new private/incognito session can sometimes resolve the issue. We recognise that this is not an ideal solution and appreciate your patience while we work towards a permanent fix.

Microsoft continue to investigate the cause of this issue, but indications so far are that it only affects a relatively small number of individuals, and can be intermittent in nature.

There is no confirmed workaround, but attempting to access the resource through different methods can sometimes yield different results. This can include:
• Accessing a URL directly
• Navigating to the resource by browsing from the landing page
• Using a private/incognito session on a web browser
• Accessing from within the Teams desktop client

We are continuing to investigate this issue.

We continue to work with Microsoft on understanding the impact and cause of the issue we are experiencing. So far there has been no indication that there is a systemic issue across the Microsoft platform, and it appears isolated to Cardiff only.

We have also been made aware that some users of the Business Intelligence (BI) service may not be able to access the BI site as this is hosted on SharePoint (https://cf.sharepoint.com/sites/bi/SitePages/BI-Home.aspx).

There is still no confirmed mitigation or workaround to this issue so far, but some users have reported success in using a private/incognito session in web browser.

We have been made aware of a number of reports of people not being able to access files within various Microsoft Teams spaces or SharePoint sites that they expect to have access to.
We are working with Microsoft support to better understand the issue and work towards a resolution, but do not have a timescale for this yet.

There is no confirmed workaround identified at this time, but using a private/incognito session on a web browser can help to avoid issues with cookies.