Is there an excuse for a 20ft Cat6 Ethernet cable to have 36μH on all wires?
I suspect you're actually measuring a lumped inductance for a single wire with your LC meter, whereas the 525 nH/m spec is a distributed parameter for a twisted pair of the CAT6 cable acting as a transmission line. Both magnitudes are unrelated.

Take a look at the telegrapher's equation and the transmission line model below:



OTOH, the calculated self-inductance of single a AWG24 20ft straight wire is 12 uH, quite close to your 9.6 uH measure.