Very few launch vehicles get off in their first launch window. There's a lot of procedures and adjustments to get juuuust right to make a launch window 90%+ of

Very few launch vehicles get off in their first launch window. There's a lot of procedures and adjustments to get juuuust right to make a launch window 90%+ of the time. The issue here isn't really an "engine issue", but an issue with putting cold gases through the engine so it's not thermally shocked at ignition-- some combination of lines and valves probably want a different procedure and thermal profile.