This appears to be related to an issue I raised a month ago - incomplete access to printer functions by Dorico.
My issue was non-standard duplex printing.
- If I specify pages 1,4,2,3, or even 1,2,3,4, all pages print singly despite the duplex settings. The hyphen e.g. 1-4, 2-3, is necessary to activate duplex printing.
Printing oddity - Dorico - Steinberg Forums