No problem, only Gigabit LAN with 8, generally use 1 2 3 6

It's okay, can be used

You measured the line is not the right way to test the line, that is to say, both ends of the cable in the cable tester on top of the end of the switch on top of the cable tester on top of the end of the wall plug in the wall plug in that end, you can plug in a The cable can be plugged into a good cable and connected to the test cable,

The crystal head in your case is not good or the wall plug is not good, the possibility of cable breakage is very low

Rebuild the line