I'm in the same boat OP, my apps don't automatically update even though the option is on. Manually updating is fine.
I tried to log a call with Apple Support but that was pointless, I will try again at some point but ask to be continually escalated till I get to someone who wants to collect logs as it could be a bug
This is happening on an iPhone 6S+ and iPhone 7+ so it's not related to the device, I've tried setting up from scratch and tried a different apple ID without much luck