Nobody has checked what the defined terms actually say
One capitalised word can be defined into meaning something the rest of the clause never suggests, and that is where the money moves.
What's happening?
Construction contracts capitalise ordinary words and then quietly redefine them. Practical Completion, the Works, the Site, the Contract Sum: everyone on the job uses these words daily, so everyone assumes the contract means what site means. Nobody goes back to the definitions section, because the definitions section is the most boring part of the document, and the drafters know it.
A definition rewrites every clause it appears in. A deadline measured from a defined date can run from a different day than the one in everyone's head. A payment trigger tied to a defined event can sit later than the event the site team is celebrating. Two people can read the same sentence in good faith and disagree completely, and neither finds out until money turns on it, because the sentence only settles once someone reads the capitalised word's definition against it.
That is usually at valuation, final account or dispute, which is the most expensive possible moment to learn a word's meaning. The check is cheap by comparison: the defined terms read against the clauses that carry money and rights, payment, change, notices and completion, marking where the definition and the assumption part company.
The solution
One pass by someone who reads these documents constantly.