It was an override issue. Not even sure why the site had any overrides. The custom field validation is now working.
With variants, I needed to define a price for each. With 6.1.0, it would use the product price for any that didn't have a variant price.
6.4.0 Backend Issues:
+ The filtering options on the Orders page are stacked. They used to be in line, taking up less vertical space. See screenshot.
+ Can the page layout features be disabled, like when editing a product? Even when I deactivate form customization, I still see some of those layout controls. I find that all to be visual clutter for normal use.
+ On the products page, the Description section flashes on and off. However, I was noticing that with 6.1.0. If I toggle to the editor, it goes right back to the normal view.
On a different note, on the Orders page, can it remember the "Display #" selection? I often find that I need to see more than 20 orders, but as soon as I log back in, it is back to 20.