You can't check in multiple SharePoint Online items in a document library

Problem

You select multiple items in a SharePoint Online document library that are checked out, and then you try to click the Check In button. However, you discover that the control is disabled.

The Check In button on the Files tab

Solution/Workaround

To work around this behavior, use Check In for individual items.

More information

This is the expected behavior in SharePoint Online when a workflow is associated with the document library.

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