I totally agree. Here’s another thought: Since we all have to start at Level 1 with the new Mass Train Pass, the game probably shouldn't even be assigning specific train-bound tasks yet. I am currently at Mass Train Level 10 and haven't encountered a single task that required a specific train so far.
It seems the trigger for these broken missions is linked specifically to unlocking that last train type. The algorithm likely assumes that once it's unlocked, you're ready for 'expert' tasks, ignoring the fact that the train is still at Level 1.
By the way, do you already have any of your other trains at Level 10? I’m about to reach Level 10 with one of mine soon and I want to make sure that simply having a maxed-out 'old' train doesn't trigger these impossible scaling issues as well. It would be good to know if this is strictly an 'SC Line' unlock bug,