Hi Rezníček Marek,
In your case, I would like to confirm what is the server you mentioned. Do you share the file in SharePoint Online sites or SharePoint server? Please let other users who are editing the file close their Excel clients to see if it works well.
If that doesn’t help, could you provide the following info for us to troubleshoot:
1.Create a same file by yourself to test.
2.Create a new file without any Macros and VB scripts to test.
3.Does the issue occur with other Office application? For example, a Word document.
4.The screenshot of the notice you mentioned.
5.The screenshot of your Office version. (Open Excel>File>Account>Product Information)
6.Share a repro file with us via Private Message .
Regards,
Zixuan