Most likely with the supply system changes, there needs to either be a higher Soviet rail capacity multiplier in 1942+ or just more Soviet railyard production. Here is the current multipliers:
26. Introduced yearly multipliers to rail capacity. Axis: 5, 6, 7, 8, 7. Soviet: 7 (3.5 in June 1941), 7, 8, 9, 10. Previously Axis rail capacity was not multiplied, and Soviet rail capacity was multiplied by 5 (2.5 in June 1941). However, rail capacity was used only for unit transport, and was effectively unlimited for the purposes of resource transport.