I have now done the 3-event sequence with Eshid to and from the Garrison, waited for her post-event dialog with HIstorian Sivvi, and talked to Sivvi 5 times. My Garrison Historian achievement still sits at 2/4. It incremented the first time, did not increment the 2nd, incremented the 3rd, and has not incremented the past 2 times I've done the sequence. I have done nothing significantly different any of the times I've done the events, and the dialogs have been essentially the same. What is going on?