I have that problem too, but I haven't DLC Industries so I think it is a more general bug. Buses and metros have less extra boarding time than trains. The long boarding times for trains is really a problem for me.

I'm experiencing the same issue and have yet to find a solution :( Though this is happening for trams for me as well.

I had this bug without any mods only few dlc so i think is vanlla bug.

I had IPT and Real Time on, and when my city reached around 50k, the problem started. The Real Time mod has a limit of 60k, but my PC isn't strong enough, so problably, this limite should be lower.
I unsubscribed Real Time and the problem is almost solved, some times the trains stay in the multiplataform stations for more than 500%, but now they depart (with Real Time on, they didn't).

Before this bug appeared the boarding took roughly 2 to 3 seconds for me. In vanilla mode a boarding now takes 20 s and the same (vanilla) train takes at least 40 s, often much longer, with IPT2. I use AVO as well. Sometimes they are boarding forever and the boarding time resets to 0% after a few thousands % of boarding time. Something is fishy . . .

I have the problem too!

I have the problem too!

+1 for the same problem

yeah i have this problem too! and i have Real Time mod. Idk if this bug triggered by this mod or not.

Maybe this will explain.
https://github.com/krzychu124/Cities-Skylines-Traffic-Manager-President-Edition/wiki/Transport-vehicles-stuck-on-boarding

Very interesting reading on Github about this boarding problem!

The root cause seems to be the core AI function. I believe that too. Real Time mod and TMPE are not affecting this. I can confirm that. The problem is there in the vanilla mode and IPT2 makes it much worse, at least for large public transport systems. Unfortunately, because it is IPT2 that makes public transport fun in the game.

I wish there was possible to just turn off the boarding phase. Thank you qwarck!