A4 B8 SLine Xenon light playing up

[Savage12]

Anyone had problems with Bi Xenon lights ?
My wife's A4 B8 S-Line Avant has just started to play up.
2 weeks ago dash display showed driver side headlight out as this was about 2 minutes from home parked car up.
Next morning no display showing fault.
This afternoon same driver side headlight out then after about 3 miles display cleared !!!
Is this the ballast starting to degrade ?

Thanks in advance.
Malc