[2020] Array index is out of range. [System.IndexOutOfRangeException] Details: No details

Looks like something related to a transport line or public transport vehicle. Let's try using the Loading Screen Mod's Safe Mode options. Before loading your save, go into Options and find the Loading Screen Mod on the left. Then find the Safe Mode options and enable all of them. Then load your save. Did that help?

Add these two mods, enable them, restart the game, make sure the Loading Screen Mod's Safe Mode options are still enabled, then try again.

https://steamcommunity.com/sharedfiles/filedetails/?id=529129546
https://steamcommunity.com/sharedfiles/filedetails/?id=1620588636

Sorry for the late answer! Christmas stole me away from Steam. :P

Hmm, good that clearing traffic fixes the error. Then it's a question of what's causing trouble for your metro. What if you make a little test for metro. Plop 2 stations close together and connect them with a straight line, then set up a line between them. Does that work?