Generally there are two possibilities:

1) A transparent insulating material such as rosin or other flux cleaning agent may be attached to the elastic piece, and it may be washed with anhydrous alcohol.

2) The positive pressure of the shrapnel is insufficient, which means that there is no contact. At this time, the impedance is relatively large, and the test instrument is not sensitive as an open circuit. You can plug and unplug several times to confirm the connection is successful.