Hey Jen, clearly it's a faulty Anova Nano, you're not the first here with one.
You have taken the correct steps.
You only need to add some frequent manual circulation of the water so it flows through Nano, OR, pour the somewhat heated water into a stock pot, add chicken, bring to temperature on your cooktop, stir occasionally to prevent temperature stratification. With Nono in place use it to monitor and adjust heat to maintain temperature.
Or monior water temperature with your usual kitchen thermometer.
Don't cook for a total combined time greater that 4 hours.
Go look for the box so you can return Nano.
When that's done contact Anova Support so they can make it right. Community is just a forum for users like you and me.
Unfortunately you have discovered the lousy quality control Chinese manufacturers provide to the rest of the world.