What you discribe sounds like a loose connection (high resistance) someplace
in the wiring to that recepticale. Just enough current is getting through
the poor connection to operate the test instrument but when you try to draw
a higher current, nothing gets through.
You should check the connection in the receptical you are testing. Also,
household recepticales are often 'daizy chained', one outlet after another..
Any receptical in the chain, between the circuit breaker and the problem one
could have a loose connection..
I had a similar problem and after checking and replacing three suspected
recepticales, I found the problem was a arched and burned contact where the
circuit breaker clips onto the panel buss bar...
Both the breaker and the buss bar were damaged and not only did have to put
in a new breaker, but I had to move it to an empty location in the panel.