Hello,
I am trying to edit a cabinet, when I zoom into the cabinet the lines which I’ve drawn on the face break up and parts disappear, when zoomed in pretty close they disappear altogether in places. It’s really hard to work around the disappearing lines! So any help would be appreciated. This is how it looks when I’ve semi-zoomed in & the problem can be seen above the handle.
Thank you 
It’s an indication that the drawn new edges aren’t exactly coplanar with the face you drew them on.
The best way to see what is going on is to upload the model as it is now.
You can inspect endpoints not being on the face of the cabinet door by measuring their distances towards the face. I wouldn’t be surprised if you see values unequal to zero.
Thank you, I’ve simply deleted those lines and draw rectangles afresh & placed them on. No disappearing lines now, wonder how I managed to draw them off the surface in the first place!
Thanks for your help 
If you click before the Inference Engine tells you where the tool is…
…You might as well close your eyes, click and hope.