Im going to dig around. Do you recall hearing about the story that while it was said Biden was in the W/H, No marine Guards@the outside door? I have a feeling these two things are related. I can tell you for absolute certainly, as an old Jarhead, that No Marine Guard would ever forget to post at that door, or forget to hang Old Glory.
So Im sure there is a story behind both..

Yes, reporters were asking about that last week, since that's usually their indication that POTUS is or isn't in the Oval.

Supposedly, one Marine left to get a Covid test, and no one took his place. Psaki said there had been no policy changes and that it's a "misnomer" that a Marine is to stand guard while the president is there.

They publish Biden's "calendar" each day, but who knows what the heck he's really doing or where he is.

It was back up this morning. I never heard why it was gone, though. It is supposed to fly 24/7.