The only speculative answer that I can think off is "access to geospatial data". AFAIK there was nothing wrong with Nirbhay's range or propulsion in it's tests. The problem was lack of very accurate geospatial data to enable the missile to fly hugging the terrain so that it would not get shot down. AlL of it's tests were done at considerable altitude over the sea. If it flew subsonically at 5,000 feet above ground it would be targeted and shot down by AAD. This is specially true at the LAC where to clear the mountains it would have to have a considerable margin of elevation to clear the mountains and consequently a high probability of it being shot down by the Chinese. The only change that could have prompted the deployment is access to US geospatial data via the BECA agreement i.e. if the US is now allowing India access to this data, then it is possible to program Nirbhay to fly via different waypoints in the mountain range, skirting peaks and hugging the terrain to avoid Chinese AD. That will make Nirbhay a viable weapon. Again, this is my speculation only.