A common cause for SSL errors is that your intermediate SSL certificates are not bundled which will result in a failed verification. One way to check this is to visit https://www.ssllabs.com/ssltest/ and review your Certification Paths.
Another common cause for SSL errors can be TLS protocol compatibility.
Pipelines 5 and higher support all common recent TLS protocols (1.0, 1.1, and 1.2 at the time of this writing).
If you find that your documents have unexpected asset failures and you're using Pipelines 1-4, upgrading to the newest Pipeline should solve any SSL/TLS version compatibility issues.