Hey mate,

It could be that you are missing one of the last 3 dungeons.

Do you have;
Keeper of the lake
Wanderers palace (Hard)
Amdapor Keep (Hard)

If it's only recently happened then i think it'll be that you haven't unlocked one of them.

They used to be the dungeons for the Expert roulette but have now moved to High since the new expansion came out.

Hope this helps!