Why didn't my beer cake cook properly?
Turning down the temperature by 20C was a good idea because of the fan, however it may be too much in your oven's case as it sounds like the temperature was a bit too low. 

What likely happened was that the fan blowing over the center of the bread cooked the center first, but the fan didn't blow on the sides of the bread as much. This has happened to me when I'm using a high sided baking tin where the bread was not up to the top. I find when baking breads and cakes that the fan tends to char the outside of things even if I turn it down, and then the inside doesn't cook so well, so I usually leave the fan off. I suggest you try the recommended temperature with the fan off and see how that works.