Chrome 56 on Slackware 14.1 requires the upgraded mozilla-nss package. Without the upgraded package you get errors on some HTTPS pages, including on google.com itself:
Your connection is not private.
with a detailed error code below:
The error comes from a bug in the NSS package. This is explained here in more detail. Slackware maintainers have released upgrades to the package. Upgrading the package and restarting Chrome fixes the error.