The problem has returned!
After some miles on the new small sprocket, now the two smallest sprockets exhibit the problem. So, it sure looks like a component mismatch or design flaw, given how many others are reporting the same issue.
I've contacted my bike shop and asked them to contact Specialized to see what they want to do about it.
I wouldn't mind ending up with a faster top gear, though I don't know what's possible in that regard.
I've got the same problem. Bought my bike (turbo vado 4.0) in november 2017. When I've cleaned and greased the chain well, there's no problem, but especially when it rains, after 2 days the chain skips regularly a tooth or something like that. Always in the highest gear. It starts with once in a few kilometres some days later it is every few metres in such a way that I don't dare driving any further in highest gear. The specialized shop changed the chain a few times and in the end I got a new chain and casette. Then there was a long dry period and I had no problems whatsoever. Now there's a longer period of wet days and the problem starts alover again. The shop (a so called Specialized Concept Store in the Netherlands) got in touch with Specialized Netherlands, but they refused to acknowledge there is a problem with the bike.
Beside this problem I love the bike, but because of this problem I and the way Specialized is handling this I now know my next bike will be from a different brand.