Bike has done about 900 miles now.
I have checked the chain with a wear tool, and it does not have to be replaced yet (but probably soon). I think Kalkhoff's recommendation is 1,500 kilometers.
However, there is an ongoing motor noise: after about 45/60 minutes, there is a fairly loud clicking noise from the pedals/crank area (once per rev). Noise stops as soon as the motor is disabled (while still pedaling the same way), so does not seem to be a standard mechanical noise (e.g. pedals or chain).
Initially, the bike was only doing that noise when assistance was set to the maximum (e.g. slope), but then it would stop. However, now, the clicking is happening on each trip after a while, even on the low "eco" mode.
A couple of times, the crank made a lot of noise (like some cog jumping), when changing the assistance level while being still (traffic light), and then restarting (without changing gears).
Apart from the annoying noise, no other apparent issues, and the bike has been going well.
Bike is now in the shop for a motor replacement under warranty. I'd rather have such fault developing while under warranty!