Hi, If the notebook in "not trusted" mode. Just click on it and make it trusted then save the file. It will work fine.

[MdMohsin98]

          Hi,

Even I faced the same issue.
Solution: Try downloading your file (this will save the work), and you will be redirected to password page of jupyter notebook where the token is required to download the file which can be found on cmd localhost section. After this, you will be able to save the notebook again and your work will be downloaded.

Originally posted by @AbhaySinghania in #922 (comment)