Running Antergos with Chromium Version 65.0.3325.181 (Developer Build) (64-bit).
I can in Firefox and Document Viewer. I can even print duplex in a Xubuntu VM running Chromium 64.0.3282.167.
Also tried using Print using system dialog and still no go.
I Googled around a bit and found some really old stuff of duplex being a default but couldn't find anything with my exact symptom.
Any ideas?