Apologies if this has already been covered elsewhere but if so, I missed it and it took me a while to work this one out. So on simulating my timetable I could see that many services were failing to keep up with the timetable during simulation. However when I ran the timetable in PIE, the trains were able to keep up with the timetable. Solution: In the Load/Unload details tab there is an option called "Completion Time Rounding Setting" By default this appeared to be set to "Rounded". This was causing many of my services to get later and later because if they completed loading at 08:05:01, in the simulation this was being rounded up to 08:06:00. With local services that make many stops this was compounding until trains were arriving up to 5 minutes late at their destinations. Setting this to "None" has solved the problem. Hope this helps someone else.
