So, the sshd_config is the same like the actual Debian Stretch branch.
Not sure but going to Debian Stretch Development could be a try.
But before doing such radical things you should wait for some others ideas. Perhaps some of the mods here will have some pity with your issue. For this you should prepare some data
- Upload a full set of logs after you have enabled debug logging and reproduced the issue; see here how to do this more in detail.
- What is the exact error within Filezilla? Is it the actual version? Enable debug level 4 and copy’n paste the last debug Infos when the error occured.
Sorry for not being more help till now.