Adding hysteresis to a window comparator
The reason is probably because Vin is driven with relatively low resistance.

If you want approximately the same amount of hysterisis on U1 comparing to U2, a simple way would be to put the equivalent of R3||R4, around 1.1K 878\$\Omega\$, in series of Vin coming in.

There is a small side effect of doing that -- it does shift the high ref level a little, which you can compensate if you want.



In my original answer above, I didn't see the easy connections to not have the positive feedback from U1 affecting U2. The connections should be Vin through a resistor to + pin of U1 and Vin directly (not through the resistor) to the - pin of U2.