Weeks 28 through 37 are a dead flat line on my chart, and in hindsight it was mostly sleep and sodium. I was in a horrible stretch at work, sleeping maybe 5.5 hours, up at 5:15, workouts gone, eating whatever was in front of me at 8pm. Scale sat at 181-183 for nine weeks.
Then it went the wrong way: 1.8 lb up in ten days after a conference with two Thai takeout dinners and almost no walking. Very dramatic for someone who had been "stalled." What actually broke it was four days off, 8 hours of sleep, dropping the salty restaurant food, and by day five I was 2 lb below where the freeze started.
Ended up 4.2 lb down over the next three weeks.
I genuinely don't know how much was fat and how much was water and inflammation, but the nine-week flat broke without me overhauling what I ate overall. If I had to bet, the sleep debt did more damage than the calories.
Compare your sleep hours the last two months to your first twenty weeks and see if anything jumps out.