In this context, I don't understand what sort of "gaps" there are or how B.1.617.2 has exploited it. The task presented by someone who has tested positive for B.1.617.1 is no different to someone with any other variant. I CBA to Google and compile a list of examples, but I'm sure a quick search would throw up a lots of examples of failings throughout the system's lifetime.
I don't think that there needs to be an incentive to come forward for testing, the government just need to remove the current disincentive. As things have been allowed to proceed, ONS data >>> anything else for this reason.
The NHS app is something I know a reasonable amount about as it's relevant to a couple of businesses that I'm involved with. IMO someone (or multiple people) should be held criminally responsible for its failures:
https://www.telegraph.co.uk/news/2021/03/04/covid-app-flaws-meant-pubs-broke-privacy-rules/