They are not on a normal network or cellular so they are subject to whatever restrictions that network has. What can wipe some folk out is that such networks can change as the IT changes settings.
If they are not on a normal network or cellular, then all bets are off about this working. As to your logs, I don't have your phones to look around.
I was on a voice call with my bf and I hung up to attempt several FaceTime calls. From my end, it said the person is unavailable after ringing for awhile. He said he received nothing, when we checked his call history on the iPhone, it was in red as missed calls. He also said he FaceTimed me and couldn't connect but phone history showed only my attempts and none of his. We both have iPhone 6, most updated software.
The "send my location" option via text didn't work for him either while this was happening. We both had no issues on voice call. 7 hrs later, no issues connecting FaceTime when we were in the same place.
How is there a record in his history log of calls he didn't receive?
Background: He claims his network is different bc it's a district work phone connected to a larger <insert tech jargon> so it's unlike my regular phone network with less restrictions. But it worked fine in the morning. Anyone experienced something similar?