Why does the tester cable not ring the first core?

Question

Computer networks

10 double identical RJ-45 sockets are installed, all cores are connected to each module and everything is wired on the patch panel in the rack. When ringing with a working Hyperline twisted-pair cable tester (HL-NCT1), the LED on the first core does not light up, but then everything is fine, and so on all sockets, except for two. With a multimeter in the diode continuity mode, the first core rings. The network is up. What is the focus?