A custom archive for WC products can set sorting options, and includes primary and secondary sorting priorities (e.g. sort by menu_order then by post title).
It works when setting only a primary sort option, but breaks (entirely) when adding a secondary option.
Other archives (e.g. custom post type archives) are unaffected, only products experience this problem.
Currently, it is not possible to add a second sorting option for WC products in archives.