I think the HL crash bug has finally been squashed. A fix is up on Github, and we'll hopefully do a small bugfix release this weekend.
As far as the Incarnate discussion goes, I may revisit the Mictlantecs in the future to give them a religious head title which can only be held by an Incarnate. The title is destroyed if there is no Incarnate, an Incarnate can create it if it doesn't exist, and a newly ascended Incarnate can choose to gain a claim on it after a successful ceremony. One reason I haven't done this already is that there are some complicated succession issues to deal with.
@TruckFeet is correct that right now only independent Mictlantec rulers can become Incarnate, but I'll consider changing it. The change might lead to interesting conflicts with the more complicated system I described above.
Yes, it was a bug caused by hard-coded antipope mechanics when any ruler has a claim on the religion head title. I'd prefer to have a more complicated system where candidates who lose the election can contest the election and gain a claim on the presidency (with a negative impact on moral authority and opinion penalties), but for now I just added a small event to silently strip claims on the presidency.