The regex engine is small potatoes in the larger scheme of things, but the reason it's so problematic is the two bigger problems in the CPPGM: the questionable

The regex engine is small potatoes in the larger scheme of things, but the reason it's so problematic is the two bigger problems in the CPPGM: the questionable architecture and absolutely insane project plan, which both appear to be "convert the spec directly into code, in printed order". This is no way to approach a complex project with serious technical risk, and willingly signing up for the death-march enterprise project from hell is the kind of thing that disqualifies you from being qualified to take on a project of this scope, let alone a grandmaster, whatever that means. You can see the outcome coming a mile away: "We cut some corners, but it's 80% done. Now all that's left is the impossible part."