In AC23, seemingly at random, and occasionally, the 3D window view changes to have a cutting plane, approx 2m in front of the camera lens. It follows the camera wherever the camera goes, and is really annoying and unhelpful. I can't continue to do any useful editing in the 3D window after it happens, because I can't get closer than 2m to an object before it starts to disappear! I can't find anywhere to turn this "cutting plane" off, and I don't even know what it is -- and if it's a bug or a "feature" that has somehow been turned on. All the cutting plane features I've found seem to assume a static cut, not one that continuously follows the camera around.
Any ideas what it is, and how I can get rid of it... and how to stop it happening in the future.
My only current recourse is to abandon the current file and load a previously saved version.
I've attached a few screenshots of a fly-in to the building, to illustrate the "effect".