Is it possible for you to provide us a Fiddler logs about the failure? To do so, you can follow the next steps:
1. Download Fiddler from here and install it.
2. Run Fiddler and go to Tools -> Fiddler Options.
3. On the HTTPS page, verify that Capture HTTPS Connects is enabled.
4. Verify that Decrypt HTTPS traffic is enabled with the ...from all processes option and minimize Fiddler to tray.
5. Run your AppBuilder client and try to build the project again.
6. In Fiddler, go to File -> Save -> All Sessions, save the archive to disk. This will produce a SAZ.
7. Zip the .saz file and attach it in the ticket.
Also, if you can share the exact plugin that you have imported, we might be able to reproduce the faulty behavior on our side.
Thank you for the help in advance.