Maybe they never managed to track down the cause of the issues. I never had them, many others didn't either, so it may have more to do with individual systems Makes it pretty much impossible to track down, especially if it doesn't occur on their test platforms.
That they repeat, not that strange imho (yet to be confirmed though). They have settled on certain programming techniques/habits. Since they're working with the same data, though on a different but similar engine, it just pops up again.
Having such a limited timespan to crank out a new engine and create all the specific data for SH5 probably didn't help either.
