If a shaft is hardened by nitriding and the friable layer is not fully removed, distinctive V-shaped scars can appear on the bearing surface after a short period of running.
Figure 1: Nitride scar in unloaded half of whitemetal journal bearing
Unless the scars are in an unloaded area, the bearing will need to be replaced or relined. In addition, the shaft should be ground after nitriding to remove at least 0.025 mm (0.001") of steel. Merely polishing off the friable layer is not sufficient.
Changing to a different bearing alloy is unlikely to be effective.