I found that the screws holding the "Optional" upper bunk frame together were loose, and upon closer examination it was clear the assembler over drove some of the screws and reamed out the self tapping screw holes. So, I decided to use 3/16 pop rivets and replace all of the screws, evidently Hi-Lo only fastens only the bunk side of the cross-members together ... so to make the frame more ridged I added pop rivets to the mattress side of the cross-members while I was at it.
Now when the bunk is lowered it is absolutely solid ... might even carry the advertised 350 pound capacity. I also drilled a hole through the wall hinges so we could remove the mattress and use the bunk for storage as described in another post. We use the upper mattress as a mattress pad for the sofa bed, it works great!