Hey,
I've built the entire fort including all buildings to tier 3 and the chapel is no exception (I've built the tier 3 chapel twice already), but the achievement seems to be stuck and not registering the completion.
The achievement is "A FORT OF MY OWN" and the sub-achievement missing is "Chapel Tier 3".
Any help would be appreciated.
There may be a display bug in the A Fort of My Own achievement. It may show you the wrong building you haven't maxed out.
Try to do T3 of other buildings. I don't know if there is an easier way to know what tiers are our buildings but I found it rather easy to know I have a T3 Command Center if I have 10 more workers than before the update. If I can swap prayer book in the new Chapel Altar, it is T3. When I have 25% more charges in my Invention Machines magically. It is T3.