From my personal experience, regularly using services on the South Western Mainline from Weymouth to Waterloo, it felt that shortly after the franchise announcement in March 2017, the condition of the 444s did decrease. The external doors got stuck a lot more or wouldn't lock, more threadbare seats than before, things like this.
I did expect it because the view I saw it as for Stagecoach- what's the point of spending money to keep them in top condition for the remaining 5 months?
The reliability of the 444s has heavily decreased, with 180,000 MTIN score in 2016 down to 100,000 in 2017 and finally 35,000 in 2018. They haven't got better since then, that is for sure!