Interesting that you say that the 6.2l has issues. I had (3) up to hard 100k in 3 years and they have been better than all my German v8’s. Better gas mileage too
Also, why would they suddenly be holding up 25s to deal with "issues" after shipping 3 model years of cars with the same engines without any pause or recall regarding any such issues, even after Car + Driver famously blew up the engine in their own long-term Blackwing?
I'm on my second CT5 V BW and have experienced no issues.
I also don't believe that there is an inherent problem with the engine as it looks like 95% or more of them are fine.
Maybe a little less reliable than most cars but we're not in Chevy Vega territory, to cite a perhaps too-extreme example.
My guess is, and this is just a guess, that there is some reoccurring problem or two with some part or two that is not being consistently manufactured or screwed into place correctly.
"Ah! It's this widget!" or "Looks like we're sometimes putting this widget in the wrong way," someone at GM might say if they figured it out.
If it is something like that, I think it could be fixed without holding back production, let alone cars already produced or in progress.