I don't think that's an issue per-say. You can't fix everything, but you can at least try to find the most likely path and do something about it. Even if it wasn't the biggest cause, you made progress towards improving some of the variables at play for the issue.
There's clearly something to learn and improve in your 5 why's. There was a hard to test feature, typos were allowed to pass through validation in the config, there was only one person making the config change and seemingly no one to review the change, etc.
Ok so all these seem like they'd contribute at least somewhat to why this issue occurred. Sure there might have been other deficiencies, like why didn't the test teams also forgot to test the feature or thought they did but didn't, etc. But you can't address everything.
So maybe you update the validation code for the config so it is more likely to catch such typo in the future. Maybe you make improvements to your config change management and enforce a 2-eye rule on config changes, and a 2 person review on the change. Maybe you make improvements to your testing capabilities so that such hard to trigger features become easier to write an automated test for. Maybe the leadership learns to inssist on planning more time for dev QA and writing tests when launching the next big feature, etc.
There's clearly something to learn and improve in your 5 why's. There was a hard to test feature, typos were allowed to pass through validation in the config, there was only one person making the config change and seemingly no one to review the change, etc.
Ok so all these seem like they'd contribute at least somewhat to why this issue occurred. Sure there might have been other deficiencies, like why didn't the test teams also forgot to test the feature or thought they did but didn't, etc. But you can't address everything.
So maybe you update the validation code for the config so it is more likely to catch such typo in the future. Maybe you make improvements to your config change management and enforce a 2-eye rule on config changes, and a 2 person review on the change. Maybe you make improvements to your testing capabilities so that such hard to trigger features become easier to write an automated test for. Maybe the leadership learns to inssist on planning more time for dev QA and writing tests when launching the next big feature, etc.