The chanel trace v2 refers to the runtime precoding feature, where the precoder is calculated at runtime based on the channel properties. In the channel trace v1 the channel is known a-priori thus also the optimal precoder can be calculated offline. The difference in performance depends on the scenario you simulate, i.e., you can not use the channel trace v1 when using distibuted antenna systems, RRHs, Coordinated multipoint feature, 3GPP 3D channel model, because you don’t know the composite channel a-priori. For the cases when it is possible to know the channel a-priori, it is known that the channel trace v1 performs with minimum loss of accuracy.
More details about the runtime precoding feature can be found in the following publication: https://publik.tuwien.ac.at/files/PubDat_239150.pdf