Problem solved.
I’ve completely removed FS from my XBox X and reinstalled it. Before installing all my add-ons, I’ve installed all the World Updates one by one and in chronological order. Only then I’ve reinstalled city updates and finally all of my other add-ons.
It’s taken me 4 days to reinstall everything (often slow download speeds (often only 2Mbps), in spite of my 300Mbps connection), but at least the World Updates all seem to be installed correctly now.