So let's get the minor(ish) bug out of the way first; sometime I'm able to see a army even though it should be covered by fog of war:

So since I don't if this could be relevant to the next thing let me just say that I'm getting some significant lag even at the lowest graphics setting; I've also tried with vsync both on and off and it doesn't seem to effect it much (though I might just be blind). For the record; this computer (laptop more accurately) was bought new early this year.

The main bug encountered was this: The player to the north and east of me had just transcended to the Zhou and sent me a non-aggression pact; so after going to the diplomacy screen for the first time I decide I should look at all the things before touching anything. While doing that the game freezes pretty bad (not the first time it had happened while playing) and goes unresponsive, but this time it starts to do something weird; the game starts flickering between being in front of the taskbar and being behind it, and on the bar it looked like the game was closing and opening again(?), but the game window itself never looked like it went anywhere. It eventually stopped flickering and I tried to alt-tab to open task manger (I keep a shortcut to it on my taskbar), but that doesn't work so I try to ctrl-alt-del, but a little after that my whole system freezes; couldn't move the mouse or anything. So after a few minutes waiting and hoping it would fix it self; I just decide to shut the computer down using the power button.

Here's the last save I have:

auto-save 39.ctr

And the last diagnostic:

Diagnostics (2020'12'16 @1435'32''496''').html