Adding fuel system cleaner to the fuel seemed to work, as per my previous post. However, sometime after, it became really bad as the engine started cutting out every few metres in Benin. I found a hotel and inspected the fuel tank. It was dirty inside, which I suspect is from very fine dust in the Sahel region of Africa. I cleaned the fuel tank, fuel filter, fuel pump, and injector. Now, after 3 tanks of fuel, I'm confident in saying this has finally resolved the issue. I've blogged more detail and the saga at http://bikingoveryonder.com/blog/2019/02/28
, so it helps others!