Creating floor/ ceiling beams that vanish

[beachdesigner]

Question about an issue I'm having with floor and ceilings beam that will disappear after creating them. If I try to "paint" or use the materials dropped to change a fir beam to be white in color sometimes that beam will vanish and turning the layer off and on does nothing, tried to "lock" the layer and still does not keep it from going who knows where....Have to constantly redraw the beams that disappear, any ideas or suggestions would be great! Using X11 Premier

 

Edited August 15, 2019 by beachdesigner
Forgot to mention software type