Bug - Getting Stuck At The End of a Turn

I have gotten stuck at the end of a turn a few times where the lower right-hand corner of the screen looks like this (note the next turn icon is disabled):

I can open the core world management screen, the shipyard management screen, and do anything else except go to the next turn.

After I save the game, exit the game, restart the game, and load the saved game, this pops-up immediately before I do anything:

This makes me think that the game was waiting for the transport to be populated, but for some reason the popup was not able to be displayed.