This is a problem that they have been aware of for a long time. I have sent them game saves where the they can see the problem happen when they go to the next turn. I do not understand why they have not chosen to prioritize this problem given how it frustrates players when it happens. I have had it happen to me twice just this week alone.
What I recommend is to hit the "Esc" key to bring up a menu, choose the "Options" button, then go to the "Gameplay" tab (screen snapshot below). Turn on the "Auto-Save" option (third one down on the left) then set the "Turns Before Auto-Save" value to 1. By doing this, when the game freezes, you can load the most recent auto-save and continue playing without losing too much work. Sometimes, the game will freeze again at the same spot, but many times you will be able to get past the point where it froze.
Good luck, and keep playing - it is really a great game with many different ways to play. Hopefully, they will decide to spend the time and money to fix all of the known and annoying bugs soon.