How to measure High-Frequency inductance of inductor using an LCR meter?
Raising the frequency to 100 kHz could certainly mean that you are approaching the natural self resonant frequency and you will get stupidly high inductance values and sometimes, if the frequency is too high it will behave as a capacitor and your meter displays nF or pF.

The natural self resonance is brought about by the interwinding capacitance i.e. It becomes a parallel resonant impedance.

I'm not saying definite but I am saying there's a decent probability given the size of the core. I'd trust the inductance reading at 1 kHz but by no means is 1 kHz a panacea.