Update for you, I found the pattern and certainly is not graphic setting at all.
If driving a train and a system restart occurs and if you then climb on to the same train you were driving before the restart is when the train will no longer load if you try hop on immediately post the restart in order to continue the trip you were on at the time you got disconnected.
If one ends the task and restarts the game client at this point you can then wait a couple minutes and then board the same train you were on previously with no issue. This requires about a 5 min wait for the BOT to move it a little ways is the best I can try explain the issue.
So hopefully this helps you guys figure out why one cannot get onto certain trains post a system restart. It seems to only affect the 4120xx freight trains. I havent been able to pinpoint others but can consistently reproduce the problem on those trains. I can certainly offer another log but after looking at it for some time it seems quite similar to the one I posted originally.
Hope that helps you guys out and thanks for trying to help me as well.