I've got an ASG (automatic clutch) Citigo and this has happened to me once when put it into R with brake on and wouldn't engage, tried again and then worked fine. It's since been to the dealers for a computer check up and all fine - as just the once on way back from Gatwick I lost power, engine still running showing in gear but no power. Stopped at side of road, waited a few seconds then all fine.
Despite a couple of teething problems I enjoy my car....apparently the ASG gearbox has a memory so if you always drive it slowly it'll respond slowly so I tend to be a bit firmer with my acceleration where necessary - but obviously still driving sensibly & SAFELY for all road users!! Fuel economy is great though car always goes into 5 gear asap to save you money. I find it a very comfortable ride, good fuel economy, good road holding and easily copes with motorway driving and steep hills....Hopefully the gearbox/loss of power issue was a one off as I'm already hooked on these cars.