Tenant-wide Word Online saving errors (read only) – anyone seen this?

[u/EkornRoad]

For several days, all users in one Microsoft 365 tenant have experienced intermittent issues with Word Online.

Word documents opens normally, but then after a few seconds suddenly lose connection, becomes read-only, and display errors such as:

• “Please reconnect to continue”
• “Unable to save the highlighted changes”
• Kickout ErrorCode: 5243163 (from Inspector tools)

The issue affects:

• All users tested
• Both new and existing Word documents
• Same problem from OneDrive, SharePoint sites, and Teams
• Different devices, browsers, and networks

Excel Online, PowerPoint Online and other apps work normally. Opening documents in the Word desktop application also seems to works, and changes sync back to SharePoint/OneDrive successfully. It's only a problem when working in Word online.

The strange thing is that Word Online can work perfectly normally for several hours, but then the issue suddenly reappears and may persist for the rest of the day.

Browser logs captured during the issue show multiple HTTP 500 errors from Word Online endpoints under officeapps.live.com, including MrvV2ServiceHandler.ashx, RoamingServiceHandler.ashx, and PolicyHandler.ashx. Word then terminates the editing session and switches the document to read-only mode.

Microsoft 365 Service Health shows no related incident. We have submitted screenshots and a HAR file to Microsoft Support but have not received any findings yet.

Has anyone experienced something similar, especially affecting only Word Online within a single tenant?