We have a SharePoint List and Libraries and recently we started seeing the User/Person field displaying the GUID and not the display name. Every time I reach the library, the column displays GUID and upon refreshing the page, it shows the correct name.
Please refer the Employee column in the screenshot, it displays the GUID and as soon as I refresh, it shows the correct name. Anyone experiencing the same behaviour in their SharePoint ONline sites.
This is the screenshot after refresh and it shows the Employee display name correctly.
FYI, everything is Out of the box, no customisations on these lists/libraries.