Experiencing this issue also. It won’t allow me to edit the number of trains or cars at all on any ride. The values are frozen. This is on custom made or already existing rides - it simply does not allow you to change the train or cars value.
before anybody answers with the generic is it block sectioned etc - this issue was evident on a go kart track whether custom made or building an existing model only one kart was allowed and the value can’t be altered.
hoping some bright spark has a fix for this