I been in IT 17 years, but quickly googled troubleshooting transfer model samples and got here. It was ok on laptop win 10 but not on my main DAW, as I saw it was git and miss below I decided to get you the solution… A few minutes of watching it try to connect and what windows was seeing I found the solution. I felt it would be the honourable thing to come back and help.
The cause is Microsoft’s built in cloud and virus scanning security features. Regardless of whether your using a 3rd party virus prog, MS will still sample cloud submissions. Just temporarily turn off all 3 features cloud, scan, tamper etc. Then Elektron Transfer will work as intended. Just turn them back on after. Tbh once you ok the transfer app it should keep working afterwards. Annoying problem, but at least an easy solution. Hope that helps anyone below. Be lucky.