Adding to Ishan's comment, We had similar issue reported yesterday where
on clicking 'Save' button, Users were getting 'Unable to Save segment
error'.Despite the error, the changes were going through. A fix for the
error has already been rolled out and the error is not reproducible
anymore. I'm not sure if this related to the error you are noticing. The
best bet here will be by creating a ticket with Client Care to know the
root cause.