Correct , my part shows up not hidden in model tree or layer tree, just not visible in graphics area .
I assume this same model opened up on another machine exhibits the same issue?
I would suggest opening up a support ticket with PTC. See if they can explain the behavior.
Try below steps (not sure whether it will work or not), if it fails create a case for Tech. Support.
1. File > Options > System colors
2. Miscellaneous > Change color for 2D Model References to some other > Ok
3. Check component display in assembly.
Martin Hanak , I tried your solution and it corrected the problem . Talked with our CAD manager about this and he to has seen this problem on few occasions . I believe it is a software bug also .
Thanks for your help