First off, a 645 with test-center disruptions is more impressive than a clean-room 645 — it shows your fundamentals are solid. Your section breakdown actually tells a clear story: Verbal at 85 is strong, Quant at 83 is respectable, and Data Insights at 78 is the one area with the most room to grow. The fact that you flagged DI as being hit by fatigue and distractions makes total sense — DI questions on GMAT Focus demand sustained attention to detail, especially the Multi-Source Reasoning and Table Analysis types that require you to hold multiple pieces of information at once.
For your retake, one thing that helped me was doing full-length DI practice sets under deliberately imperfect conditions — with background noise, after a long day, etc. It sounds counterintuitive, but it builds the mental stamina you're describing. Also, for DI specifically, practice triaging: quickly identify which sub-questions within a set are "gimmes" and which are time sinks, then tackle accordingly.
You're clearly close. A focused DI push could realistically put you in the 680+ range on a retake.