The same issue was discussed here: https://github.com/pnp/pnpframework/issues/336. Windows 2012 R2 and worked intermittently.
Make sure the server supports one of supported cyphers:
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Hi Michael - I verified with my admin the DisableCustomAppAuthentication is set correctly. We even set it to $true, waited 30 minutes, and set it back to $false. This didn't help. However, the article you posted is very helpful. I'm looking into it now. I was bit by the TLS 1.2 change a couple weeks ago. I updated the application to .Net 4.7.2 and it was working fine. It it running on Windows 2012 R2 and I suspect I'll find the wrong ciphers being used. What is quite odd is that it will work intermittently.