Energy balance

During the refeeding phase after caloric restriction, initial rapid weight regain is predominantly water retention, while actual fat and protein storage occurs more slowly and may be masked by continued water loss in later recovery stages.

When you start eating more after a diet, you will see the scale jump up quickly. Most of this is water, not fat. Later, you might see the scale stall even while you are eating in a surplus, because your body is rebuilding tissue while losing water. Trust the process, not just the scale.