I am having the same problem with this world:
https://www.worldanvil.com/w/travellers-anonymous-lenp
I was able to export it until 2 Apr 2026 but not since 9 Apr 2026. The symptoms are as described above: For this world, when I click Start it doesn't show any progress messages and it does not get exported.
I am still able to export at least some of my other worlds (I haven't tried all of them recently).
I would really appreciate a fix for this because I would like to have a recent backup copy of this world.