Literally the exact same thing happened to me. I lost 15 lbs through the first 9 days. Then my weight went back up 4 lbs, and finally today it went back down a couple. Gaining the weight back happened right when I went from full liquid diet, to a puree diet.
It has kind of freaked me out, especially since I have been able to handle so much pureed food, about 1.5 cups at a time. The only thing I can figure is that I got really dehydrated by not tracking my water close enough. I'm now determined to track my water, protein and calories much closer. I'll let you know what happens.