If one of the 3 chains themselves are not actually skipping on a chainring or a cog, I would look at your cassette freehub and the ICS double block freewheel mechanism as possible sources of the slippage.
We have enjoyed 19 years of trouble-free miles on two da Vinci Joint Ventures with only the usual regular maintenance.
Last edited by Joint Venture; 07-30-20 at 01:33 PM.