You are correct in saying EIT's should be in the session layer.
My route is not large but is very intense. It is around Carlisle in the late 1940's when it was in full swing.
It has one major station with 7 double or quadruple main lines radiating from it with another 13 stations on those lines.
It also has 10 large goods yards and 6 loco sheds, or 7 if I roll it back to the 1920's.
To control all of this I have 68 EIT's but can't remember the number of paths but it was well over 500.
I am running 22+ so I can pause the session and resave as the next session. I run the sessions for 48 minutes, pause, save and then run for the next 48 minutes etc.
I am working to a working timetable for passenger and freight for 1953 and traffic is fairly intense plus all the associated shunting in the goods yards where each yard has at least one shunter but most have two.
So, as you can see I have a lot of drivers and locos in each session. I got to about the tenth session before I started having problems, first paths started to disappear form an EIT and I got around this by resetting all rules when starting that session but then it came to the point that the session would not load.
So, here I am looking at alternatives to cut down on the amount of data to see if I can get any further.
Peter