I just read another post talking about when elements go missing ...
http://archicad-talk.graphisoft.com/viewtopic.php?t=47548
In it Link mention an option to "Hide Cut Elements".
It took me a while to find it until I realised it is an option in the interior elevation settings (I don't use interior elevations).
But I am guessing you have ticked this option by mistake.
Barry.
One of the forum moderators.
Versions 6.5 to 27
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11