That's awesome Vet! +rep
I'll crank up my save when I get a chance, but I'm sure it will work.
I have not seen the spinning cursor myself since the last patch, which is at least three years old. Indeed, the main problem was agents stuck on bridges because of their low movement and long length of the bridges. But with the new higher movement of the agents I have not seen this again.
If it still happens, then go back to a save and check for an agent stuck on a bridge with the fog of war off, then go back again to the save and move him with a cheat. Or change the movement of that agent (or all agents) in descr_character.txt for a turn and reload the save. Of course one has to restart the game every time a file is changed so that the game is recompiled.
I have these errors sometimes
I have this error sometimes