I am Archicad 25 on the student licence, I have just been amending my site and suddenly my walls have disappeared. I have tried to get them back via the layers, however, nothing I have done has fixed the issue. Any Advice or support is welcomed! I'm racking my brains as to what I have done that has changed it.
I know they are still there as when I select the wall tool their frame is selected.
There might be invisible elements interacting with those walls (Try setting the layer group index of the layer that contains the walls to another one, or 0 - if it's zero it won't interact with any other element)
Then if that's the case, you'll need to see which elements are those interacting with the walls. Did you place large slabs on top of your model for testing purposes? Or duplicates of those walls which aren't being shown at the moment? In case you did, try putting those elements' layers in another layer group index. (Layer group index are view-dependant, should be updated in every view)
I maintain those Solid Operation purpose only elements all in a same "work layer", which should be in the group index 0 in all views, so they won't interact with anything and can be hid/isolated altogether