Strange flickering on dynohub front light

Dynohub: SON 28 | Front Light B+M CYO T Premium 1752QTSNDI

The set works just fine until recently I move these to a new frame. can notice intermitmment flickering (lights get dimmed for a split second say 100ms), irregards to any speed level above 15km/h and it's not linear to dynohub spinning rpm.

Standlight is OK. connection seems to be secure. This set is a bit over 2 years old.