If it goes to zero when something is plugged in measure hot to ground and see what voltage you get. If you get voltage to ground then you have a neutral problem.Leave the meter connected and plug something in and see what happens to the voltage reading.
If it goes to zero, go to the panel and measure the voltage at the breaker. Then measure it at the mains again. All the while with the load plugged in and the receptacle not getting power.
Report those results.
We can't be sure the neutral is the problem until we see that reading. That's why I included it in the mix.I measured the main but I forget the result.
I replaced the breaker and the receptacle last night, and tried the breaker in all available slots. Same result. I have not tried already used breaker slots.We don't know it is s neutral problem. That is why I asked for a measure to ground as well. In fact since it drops at the breaker as well it is likely not a neutral problem.
You could try swapping the hot wire with another breaker of the same value.
This is a sub-panel and the feeder neutral will still be in the suspects we are rounding up.In fact since it drops at the breaker as well it is likely not a neutral problem.