I am skipping spoilers because this is on my to-read list - in fact I read the first chapter but the mood in it didn’t suit me at the time, so I picked up Their Finest Hour & A Half instead (and enjoyed it but had qualms similar to yours - I do not think the romance that was cut short was all that convincing, actually). I really liked her kids book Wed Wabbit and possibly romance is just not her strength? I also liked Odd One Out but again for friendships rather than romances.