Although I agree that room service by 6pm is unusual and they should have done this between 10am and 3pm - although I think there is no fixed rule for that, just an 'expactation' I would have.

Anyway, if you feel the need to complain about it, contact the GM (google "general manager radisson blu dublin", first hit on linkedIn.ie, then [email protected]), personally I wouldn't make a big fuzz out of it and let it slide... an unserviced room and lame excuse from the front desk is nothing I would pursue.

They probably just missed your room and didn't had the guts to admit it, perhaps fearing you will hunt there for compensation? Which based on this thread sounds not that unlikely

In general the RB Dublin is a great property.