Due to the fact that you have seven 2D xrefs, i am wondering if this is an issue i had years ago where the progress bar would constantly say "scanning the drawing". With the new interface it could potentially be the same problem, but without the old visual characteristic. Verify that your "SHOWLAYERUSAGE" variable is set to zero.

If it isn't that then I am not sure and i would have to suggest opening them with the "RECOVER" command and/or open them up (wait the 20 minutes) and once open use the "AECTOACAD" command; just hit enter throught the prompts. This will create an identical drawing prefixed with ACAD. I am not real sure what it does, but I have fixed a number of drawings by doing that. Then there is of course the option to just Copy/Paste all the objects into a brand new drawing and see if that drawing recieves the issue.

try all that... may have some luck...