The flash models, for coding are reckless in my experience. I have a Ultimate subscription, get good quota, but still use Opus 4.6 as it's much more reliable if you manage the context window carefully.
You need more safeguards for sure, but also it tends to fly off down rabbit holes, rebuilding things in dumb ways, hacking around things, making assumptions etc, it seems very eager to go 'ta da! I did it look how quick I was', sometimes it nails it other times it created a lot of tech debt.
Also if it ever says, "I've found the root cause of ..", it definitely has not found the root cause and is making a non evidence based guess as it has run out of ideas.