KONNEKT users may see a grey "X" on file and folder icons in Windows File Explorer.
This is no error or problem. You can still work with your files without of any restriction.
This is a visualization in Windows Files Explorer of a setting that KONNEKT folders and files have, to save bandwidth.
The setting in called "FILE_ATTRIBUTE_OFFLINE". It indicates to the operating system, that this file or folder is not available immediately. As a result, the Windows File Explorer does not generate previews for the files.
We use this setting with KONNEKT files & folders to save bandwidth between the client and SharePoint Online.
The visualization is not visible on every client.
If you want to have more details on this setting, have a look here.