Was this a clean install or did you overwrite DF with another DF? Or overwrite any of the files or have duplicated RAWs? But, in your case, its probably something related to sites and armies.
Clean install. I think I migrated one set of save files from 40.12, though.... Could this have done something?
In the previous version I was getting tonnes of goblin attacks, but in this one - nada.
Define "high population". Proper sieges will never come until you reach 80 dwarves. This is a fact.
More than this on each of of the four embarks. Plus, I usually get baby snatchers and the like well before ~80 dorfs. :/