Problem:
Unable to edit Office Document in Signals Notebook
Solution:
This behavior may be not specific to just Signals Notebook, and can be reproduced outside of our application. To verify, close Signals Notebook, and try to to edit Office Document in MS Office Online. In some cases, the problem can be solved by clearing the browser cache.
There might be cases where a message saying that User (ABC) receives a lock message saying (XYZ has kept the file open) while opening a excel file. The file is already closed within the system both online and in desktop but still the pop-up window comes. If so, check this link that explains what the issue is and how to fix it: