Kalkhoff Belt Drive slipping.

[Damien O'Sullivan]

My Kalkhoff Integrale (2017) has already had its motor changed out under warranty , with the past few weeks I have noticed while cycling that the belt spins out without any traction , i.e. I'm peddling and going no where , eventually after a few seconds the belt catches again and I can continue on my journey.... It seems to happen to me more so from a stop start position but can also happen while I'm cycling along normally when changing up or down gears ??
Quite an issue if I'm cycling in city traffic as I have found myself at cross junctions in traffic in a "spinning class" while the belt isn't catching ??

Any HELP suggestions would be very much appreciated... I only have 3975Km on the bike so its relatively new....