Partially Working Lights on Pre-lit Tree?

I have a four section pre-lit LED Xmas tree. After five years, the top two sections remain fully lit. On the bottom two, some branches light up and some don't. If a bulb is removed from a branch that lights up, the rest of the lights stay on. Each plug for each section lights up some branches. I have changed out the fuses in each plug and still some branches don't light up. I have checked the wires and can't find any damage. Any suggestions?

By Randall