This is a REALLY bad bug as it's behavior could cost me a game (especially at higher difficulties) and very much needs to be addressed!
-Cities are self terminating (self destructing)
-Build queues are mysteriously replicating build items
-Random audio of pillaging/destruction occurs
-all three are somehow linked together...
Bug appeared after a good 2.5 to 3 hour gaming session. It occurred abruptly a few turns after Blood Season was declared, at which point the Magnar civ resigned from the game. This caused their remaining two cities to disappear as normal. Within 2 to 3 turns later I had a pioneer go claim a choice spot where one of their cities (or within one adjacent square) originally stood.
Afterwards, this new city -Dundian, will spontaneously remove everything from it's build queue after a turn or two. If you rush build an item or the gold mine, within a turn or two it will self destruct! On average within 4 turns or less the entire city will self destruct leaving whatever military units guarding it intact on the map.
A nearby city of Ryss (a captured Magnar city) has the tower of Eurog (or whatever) replicated multiple times in the queue. If you remove one you remove all of them and start the building process over!
If you march my nearby armies into Umber territory (north west of my borders) and conquer their cities....these same bizarre failures will "infect" each captured city.
The problem revolves around territory previously occupied by the AI civs.
Multiple reloads, reboots, etc won't recover from this. Additionally this is a brand new computer, and a fresh install of FE, and the very first new game.
One thing that might have something to do with it......I am reusing very old save files by overwriting them. The original save files were almost exactly 2 years old.