Clignoteur is not stable
When the clignoteur is blinking unstable there can be a few possible causes; when the original BMW clignoteur is still used it could be a good idea to (carefully) open the clignoteur and resolder the components.
The clignoteur, which by the way resides in the headlamp, is constantly shaking and therefore it's not so strange that the soldering points are becoming bad.
An other cause of instability is that the original clignoteur is replaced by a cheaper brother without internal voltage regulator which blinks terrible.
(c) W.P.Barendsen 1999