The XSRF error historically happens when working on resource constrained hardware. For example, I get it sometimes on my 6 year old laptop, almost always on my crappy virtual machines, but never on my full desktop.
The only thing that’s coming to mind regarding the verification error is that we’re back to something not being set up correctly or taking too long on your SFTP server. I apologize if I missed this in your posts, but did you ever update from the beta to a canary version?
I ask because if the issue is simply timing related (your SFTP destination doesn’t respond to Duplicati fast enough) then you might find the --http-operation-timeout parameter in the the newer canary versions worth testing:
Though I’ll be honest, I’m not sure that applies to a socket read timeout…