I think it did give the message that the homeport had been updated, but maybe not. Can't remember now, but I usually make sure it has. however, I was only flying a few feet away to take a photo so may not have worried about it. I haven't found any advice on the DJI website related to the Mavic 3 where it is suggested that you should check if the map arrow and ground direction are the sameThis is why a pilot should check drone arrow orientation on the map, to the actual drone orientation on the ground before take off (when GPS mode is active), and why the lady always says "Home point recorded, please check it on the map."
Having the low magnetic influence causes this interference (and not give any warning).
It doesn't put the drone into atti mode, it just causes the drone to fly off whiele attempting to adjust corrections, totally the wrong way, usually a very fast path, no control, generally until signal is lost, or a crash happens.
A true flyoff but totally unavoidable.
I have read that it can correct itself in a short time in the air, one or two cases I think in the crash section threads over the years . . . but usually this doesn't happen fast enough.
If the map arrow and ground direction are different, all you need to do is shut down, move the drone a little to a new take off point, and try start up again.
This usually fixes the issue.