Abstract
I tested the IFO state flag works well or not in various interruption.
It was able to detect interruptions of observation mode.
Criteria can be found in JGW-G2314964.

Details
This test was done in READY state not OBSERVING state.
READY state is same condition as OBSERVING state except a value of K1:DET-OBS_INTENT.
In READY state IFO guardian shows the notification that OBS_INTENT is not enabled as shown in Fig.1.

In the case that SDF differences are not 0 at least one model, IFO guardian cannot stay in READY state and it goes down LOCKED state.
At the same time, SYS_SDF guardian also informs that which models have differences from the SDF setpoint as shown in Fig.2.
And also, when the loaded SDF table is not a 'observation.snap', IFO guardian goes down LOCKED state
and SYS_SDF guardian shows the fact that SDF table is different from the 'observation.snap' (See also Fig.3).

IFO guardian also ensures the absence of excitations from the excitation blocks or the excitation channels on the FilterBank block as shown in Fig.4.
In this case, SYS_EXC guardian shows that which model makes a excitation.

Finally, I confirmed that the absence of the calibration lines makes non-observation mode (See also Fig.5).
Though there is no special dedicated guardian for this issue, Pcal and/or VIS guardians also informs the absence of calibration lines.