I don't think there was an update in January.
IMO train races started when dirty air was removed and simply nerfing DRS will do nothing. Maybe it didn't manifest itself right away because the tyres were tweaked at the same time so for a few weeks we had the novelty of managers trying different strategies which masked the underlying problem. When the new tyre characteristics were understood the strategies converged and trains became a thing.
Two circuits with very low DRS power that spring to mind are Turkey and Belgium, yet in my experience these circuits play exactly the same as the other 22, a train of cars all on the same tyre strategy culminating in a final lap boost war. For this reason I'm not convinced that nerfing the DRS would make much difference.