The only thing that i know about it is that I was having trouble shaping that part of the roof, and I kept trying to reshape it by the vertices and it would just dissapear when i moved the vertices... like i deleted it. And I tried that a few more times and then gave up and made it a different way. And I think that must be one of them that dissapeared off the screen in the editor.
odd..thats a concave shape. i thought those couldnt exist? unless its actually more than one brush. .
. .i doubt this is the case, but maybe youve got something in scripting? are you trying to make that building explode?
I'd go into radiant and draw a box around the area and do a 'select inside' and see what shows up then delete all the showing pieces. I've had similar things happen when dragging the V-vertices. Best bet is as soon as the image vanishes is to NOT let go of the left mouse and drag it back out quickly. IF that fails, use the 'select' touching or inside options to find it again.
every time i re-compile, it gives some more errors ... i get a brush number and "degenerate plane" or somethin like that... and under it will say "floatplane: bad normal"
Draw a box around it, select 'inside'
Delete
RECOMPILE and look for more errors.
If none, copy and paste the elements from the other window. Do some compiles WITHOUT the structures, need to be sure that's the only problem area/brush(s)