Time will tell, but I'd put my money on a lot of undiscovered cases in Europe and the UK. Vaccinations have mostly been in elderly people who are at high risk of health complications anyway, it's only recently that younger populations started receiving the vaccine. And Norway is among the most paranoid of these countries, with good health data and monitoring.
Norway has also had at least three serious cases with 130.000 people vaccinated, so the incidence is certainly higher than 1 per 2.3 million.
At this point, with a plausible mechanism of action being discovered, it's either that or a "bad batch". But this doesn't seem like the kind of problem that would likely be caused by contamination or bad ingredients, and there's been enough time by now that the batch numbers behind the cases will have been thoroughly checked.
This will be a very tricky ethical consideration, with not only weighing different risks between different age groups, but also the public's trust in vaccines and the advice provided by health authorities.
My money says that AZ will be pulled from countries with few Covid deaths and/or other vaccine options available in the near term. And some controversy in countries that do not meet these criteria.