I got my EE in 1966. I retired in 2007. Two old farts.
I would probably take out the cap and see if it still acts the same, but that's just me. You could also go by the old adage, "If it works, don't fix it.".
Hysteresis is calculated by simple math. It's just the change in voltage at the noninverting input when the output switches. In this case, first calculate the voltage swing at the comparator output. Since R6>>R5, you can safely ignore R6 for this calculation. The swing will be from ≈0V to ≈1.4V, or about 1.4V p-p. This gets attenuated by the network consisting of R6, R9, and the resistance looking into the pot wiper. The wiper impedance varies from zero to about 8k, depending on where it is set. Thus, your present hysteresis is approximately
Vh=1.4*((R9+Rpot)/(R6+R9+Rpot). This calculates out to be a range of 88mV to 150mV.
Actually, the circuit won't trigger when the wiper is at max voltage, but simulation shows Vh=152mV with the pot voltage at minimum, almost exactly what I calculated.
If you try to leave R9 at 10k, the change in pot resistance will cause your hysteresis to vary even more wildly if you lower the value of R6. That's why I suggested changing R9 to 100k.