I am also having that same issue. I try the code and get nothing back. I have tried it in the product templet liquid code and in a by adding a templet liquid block. I can get a product metafield to show, but not a variant metafield. I have check to make sure I have a value in the metafield and triple checked the name and key. The “Primary Voltage:” show up just fine.
**Primary Voltage:**
{{ variant.metafields.spec.pri_volt }}