A likely cause of this problem is the misalignment of the Nuvinci hub. The hub can become cocked at an angle which can, in turn, unseat the chain from the cog. Look under the vehicle to check the hub’s alignment. The hub is the smaller of the two black cylindrical drums located underneath the floorboards of the ELF.
To remedy this problem, which is most likely due to loose hub bolts, align the chain and then tighten the hub bolt nuts. The hub bolts are the two bolts that hold the hub in place against the frame of the vehicle. The hub bolt nuts are 15mm in diameter and can be tightened with the appropriately sized combination wrench.
If the hub is securely fastened, then the chain tensioner(s) may have become deformed. If the chain tensioner becomes bent then the chain is again at risk of becoming unseated from the cog. Check for this issue by examining the chain tensioners, which are the two metal arms with black wheels on the ends that hang underneath the rear portion of the vehicle.
If the chain tensioner is bent, then the tensioner arms must be replaced. If you would like to purchase new chain tenstioners, then take a picture of the chain tensioners on your ELF, fill out the Parts Request Form – https://organictranstg.wpenginepowered.com/parts-requests/, and attach the picture to the form.
