Brian and I have plotted the beginning of the (bad) excitation in dataviewer in both the ISI and IOP models. We have also plotted the GPS time according to the ISI model (DCU_ID 75). As you can see, the GPS time drops out when the model is being off, but comes back up shortly thereafter. This data is for the 11:42 UTC restart when the excitation starts.
We plot the same for the second restart, twenty minutes after which the fiber break occurs. We see the same thing - the model is shut down, then starts again. We see a similar drop in the GPS time to 0 before the model restarts. The excitations also stop when the model stops, and start again when the model restarts. We see a growth in the amplitude of the coil drive signal as well as the DAC signal from the IOP.
This is not inconsistent with a loop instability within the model.