I have been using MIN's since the beginning of Trainz. By now I do it fast as a routine, and in many stances I have written here instructions of what and what not to do. So, I have noticed, with any MIN, that there is a maximum number of commodities it can carry. On some industries I have let my hand go and populated it with 12-16 or more commodities, and also have the carrier wagons made to accept the same commodities. The train arrives, stops and continues, not loading or unloading anything. I suppose that there is a maximum number that can be used. It does not matter on the quantity, 1 or 256 items/units, it matters on the number of asset-commodity. Understanding that they are not faulty as they would operate normally when used on less populated MIN's. So, the question is how many is too many? Way around this is to use several short tracks each populated with a reasonable number of commodities before you get into trouble.
A variation: We can classify invisible platforms for passengers as glorified MIN's, where you can see the people appearing and disappearing magically when a train arrives. I have no problem setting these. On the AJS's ones, the setting that works better for me is to set it as "Through" and "Terminus", irregardless if it is a passing-by or final destination. Here is the twist: On your route, how many stations do you have? I found that if you, again, have way too many, and there are "too many" AI controlled trains doing all kind of things, at some point trains will start missing stations, whether you use "drive or navigate to". (they will also start doing silly things here and there, and running away when they should not, even if before they did obey all the commands on the same location).
All this gets me to think that we (or at least me), have reached the upper limit of what is considered a reasonable working/performance on the product. However I have to say, the sky is not the limit, and to me being below that threshold is quite acceptable and satisfying. But we should know what is the limit of that sky. I use a high performance platform, so hardware should not be the issue.
the maimum