That sounds very weird. I cancel Plus tickets quite often. Just today I cancelled a Plus ticket which was a no-show (I did not show up at CPH airport because my meeting was cancelled). Got the entire ticket refunded without any issues.

I think it is more likely that somehow SAS screwed up the rules they are showing to you, rather than this being an actual change. It would not make any sense that Plus tickets (which are the flexible product of SAS) should not be refundable!

EDIT: One exception are Plus Saver tickets on IC routes. Here it costs EUR 300 to change or refund the ticket. But you also save quite an amount on Plus Saver compared to Plus on IC.