Hellenic League reform bug?

I have already successfully reformed the Hellenic League much earlier (around turn 70-80 I think) and have Greek League Member State governments in many cities, but now I have this pop up at turn 281 (no effects whatsoever though). Maybe this is due to the automatic trigger for the AI (and slow players )? Also does the reform now require 4 Archons to stay in Korinthos for only 1 turn? Because I remember being able to build the Sympoliteia immediately after gathering the Archons the turn before.

Save included (unmodified 2.3 except a music mod). Press end turn and the next turn you will see the pop up.

I'll have to check the automatic trigger and fallback. EDIT: Yes it's the fallback, I'll update it.

You don't have to gather them in Korinthos at all, any more, just own Korinthos and have four State Leaders.