A family of Microsoft word processing software products for creating web, email, and print documents.
Nope, Word comes with an Edit menu out of the box.
It's just that there are commands that some of us have added to it or re-arranged.
I was thinking that it was any customization that made Word fragile, but perhaps it's even specifically the Edit menu. However, as you reported, it could well be related to complex tables.
I'm convinced that modern full-scale software (not just Word, but also OS's) have become too complex to be managed well and that with the complexity comes uncertainty, crashes, etc. The fragility has increased--with far more ways of hanging the software. Perhaps it was always there but with millions more lines of code, quality control is impossible or, rather, much, much more difficult.
Of course, it doesn't help when new organizational schemes and approaches are introduced--e.g., how Find/Replace works.