USB signal drops at low temperature
The signal, as shown, indicates that you have a AC decoupling somewhere in the USB high-speed transmission line, since each of D+ and D- signals (to the left on the screen) seems to be switching into positive and NEGATIVE area relative to common ground. The HS lines should be direct connect, no DC blocking caps as in USB3.0 signaling.

In normal HS signaling both D+ and D- only swings from ground and up, not into negative area. There might be some undershot, but not to the degree shown on the oscillogramm.

EDIT: frequently this kind of odd signaling and all sorts of unstable behavior happens when the bottom slug on the chip is not soldered to a PCB pad, which must be connected  with multitude of vias to a solid signal ground plane in internal layers.

EDIT2: This is not an eye diagram as defined per USB-IF specifications. Please refer to this Agilent/keysight document for necessary equipment (test fixtures) and correct procedures. It is unclear which pattern is shown, from host, or from hub, or after hub. In any case, although the signal is not statistically averaged per USB specifications, there is one "red flag": the trace #2 shows average frequency as 239.62 MHz (assuming your scope is factory calibrated). Thus the deviation from the nominal 240 MHz is 0.4/239.6 = 0.001669, or 1669 ppm. This is more than 3 times outside the required 500 ppm. It is likely that the temperature change results in too much of frequency shift, which goes outside the extended tolerance of host receivers. Check the stability and phase margin on the crystal oscillator that feeds the USB hub.

EDIT3: regarding the USB protocol analyzer, if you want to debug USB 3.0+ traffic, I know of only two instruments, Ellisys Explorer 350, and Teledyne/LeCroy Advisor T3 (on affordable end of models, $2,500). If you want to limit functionality to USB2.0 only, a couple of instruments are available, starting with Beagle USB 5000 for $500. But you will need to get one-two years of practicing and deep knowledge of USB protocol to make sense out of the traces, and make correct interpretation of bus events.