ZRH seems to be a bit problematic with OW in general. I fly BA with my AY Emerald card and I always have problems accessing the Bellevue lounge. I have worked out the reason for this...
The staff member picks up card and boarding pass, reads Y on BP and interprets as no access.
Proceeds to look at the card, which says AY.
Turns to her computer and looks up AY (and not BA, which is the heart of the problem). This says - AY uses Skyteam lounge in terminal X, no access to Bellevue.
At this point I have to politely advice the dragon to open up BA info and read at the bottom of the page where it says: OW Emerald OK with any class ticket when flying with BA... usually takes about 5 minutes...