After taking Dourdan nothing happened. No "mission finished" and no new tasks were assigned.
After a long time of searching the town I decided to drive to La Trinite.
In La Trinite I found a APC that was stuck on the fuel station.
After I destroyed this APC the mission was finished.
I have saved the game before the final push into the city (but after the first wave of tanks coming from La Trinite) and tried to load the save game several time and the mission did never end. I assume that the APC was already stuck at the time I saved the game.
In this saved instance I was able to reproduce this but I did not play the mission twice and did not try to load an earlier save game.
I will have a look at it. Though it would be good if you could revert the mission and test it if the issue persists even after reverting. Otherwise it might just be a one time thing.
This mission is long and I don't plan to play it again and I assume that it does not happen often that the APC gets stuck so badly that it fails to continue driving. But obviously it can happen.
Imho this missions needs an additional trigger to end the mission if no enemy units are present in the city for some time. I assume that the current trigger is "all units are destroyed" but this does not capture the case I encountered.