Electricity "disappears"

Hello forum community, I have the following problem: I have a fuse in the bathroom to which a clock radio is connected. Actually, I intended it for a dryer. Now it happens that suddenly no power flows when the radio is connected, without the fuse "tripping." If I turn the fuse off and on again and then hold a phase tester to it, it works, but when I connect the radio, the power goes off, although the fuse remains "on." The indicator does not go out abruptly but fades quickly. The contacts in the socket are tight, I have checked that. I have now connected the socket to another fuse (washing machine) in the fuse box, and everything stays as it should. The only strange thing is that I only rewired the upper cable; I left the lower one as it was. Could the circuit breaker be defective?

It may be that the electrician did not tighten the screw on the circuit breaker at the supply side properly. You won’t believe how often I have encountered this.