We train to attempt a relight if there are no signs of damage, such as fire, seizure or vibration. Auto-relight will normally restart an engine due to a simple flameout. A flame out can occur when the combustion process stops due to things like Fuel starvation,Heavy rain, icing,ice crystals,Engine stall...etc etc. A relight is not always 100%!!!
I've never had a successful relight when in the sim. Therefore carried on with ECAM actions. Found this video useful on youtube of Engine Failure as I was struggling going through the manuals.
https://www.youtube.com/watch?v=KyWBCiQYRVM&t=206s