Issue with TI comparator
Now fixed. The LMH7322 has ECL outputs. It is capable of providing LVDS levels, but this is not true LVDS. The outputs therefore need termination to ground (or another voltage below VCCO-2V).

I replaced the single 100 ohm termination resistor between the outputs with two 50 ohms, each to ground, and now the output is as expected. There are therefore a couple of problems with the model in the simulator: the device works fine with VCCI at +3.4V (as in first figure) and the model does not model the outputs as ECL.

Thanks to all for your comments.