When importing discounts which are each being added to multiple discount groups (in the dgroup field), the discount are imported and they correctly show the multiple groups in the Discounts list. But they don’t work on the live site, and when editing one of these discounts in the back end the discount groups field is empty.
The list of discount groups is comma-separated, and I’ve tried with and without spaces around the comma, and also made sure the character case is the same, but it still doesn’t work.
Indeed, the whole string is considered as the name of 1 discount and in fact won’t work. I forgot to convert the discount groupnames to ids when importing (used to be accepted, but when I started allowing multiple groups for a discount, this was changed to just ids).
This change should fix it: https://plugins.trac.wordpress.org/changeset/2757962/
but the quickest/best would be to use the discount group ids.