After a few days of debugging and trying different options this particular SCORM is now working. i.e. it is sending the user's completion to the LMS and it's being recorded.
What did I find out?
Use Course Attainment for completion in Evolve when you need a clear, reliable completion signal (less fragile than “All Page Components Completed” when components have hidden/implicit requirements).
Avoid custom pop‑up/redirect on exit that can interrupt the last Commit/Finish calls. Let the course set completion, then close cleanly.
Validate in SCORM Cloud first to confirm the package itself sets lesson_status = completed before testing LMS nuances.
Provide a visible end screen with an “Exit” button and clear instructions—this encourages a clean finish and reduces lost completions.
Enable Totara SCORM API debug to confirm the LMS receives lesson_status=completed and a final Commit before Finish.