How many Sonos endpoints do you have? Some of us have seen an issue where if you enable more than 7 Sonos endpoints then the latterly enabled ones will not be selectable as zones to play music thru (and it will interfere with enabling and selectability of other non Sonos zones). See Roon 1.8 (Build 880) Feedback Thread - #61 by Eamonn_Maher
(sorry if this is not your issue)