Sorry I hit reply too soon. @Rennbird the same thing happened with my dd2. Got some good 5-6 hour stretches then 3 hour blocks, I was cheering but around 10 weeks it all turned to poo.
I want to tell you dd2 improved on her own, it was a phase etc but unfortunately it didn't here. I did some sleep training at 5 months as sleep continued to deteriorate to the point of 6+ wake ups, I was desperate and had an exhausting 3yo to deal with.