I'm having very similar issue with filezilla. I've been using SFTP successfully for 5 years. Now all of a sudden it stopped working.
1.I'm able to login on different computers and networks without any issues
2. I'm able to login using terminal to SFTP with credentials successfully.
3. I've tried turning off firewall and anti-virus and did not resolve my issue.
Any suggestions. This is definitely a file-zilla issue. But, what could be going on to block my connectivity.