(just in case)
Variac with a case, a bit over 30 liters, I think it's a TE.
(meters are mine, with Dremel, iron was thick)
(decades old drill bits couldn't really do it)
BTW,
I have also one of those splitting RJ45/RJ11 testers, not so fancy looking older model, and it is not showing all errors.
Possibly something to do with regular LAN pins vs. others, can't check, the device is currently out of site.
If memory serves connecting pairs 3 and 4 only is too exotic.