Data shows 618,903 alerts were sent - a 17% rise from the previous week.
There are complaints from businesses that the alerts are causing serious staff shortages and affecting services.
However some fully-vaccinated key workers will be exempt from self-isolating if they are pinged by the app as a close contact of a positive case.
Business secretary Kwasi Kwarteng told the BBC a “very narrow” list of jobs would be released today.
Self-isolation for all fully-vaccinated people pinged by the app as close contacts is due to be scrapped by 16 August, although there are calls for this deadline to be brought forward.
The app alert is advisory only and not enforceable by law, unlike a phone call from the Test and Trace team.
"If you are pinged, you should self-isolate. I know it poses challenges, and we are seeing reports of shortages which we are monitoring, but the rules are clear and I think they should be followed," Mr Kwarteng told the Today Programme on BBC Radio 4.
Latest government figures show there are a further 44,104 daily coronavirus cases in the UK, with 73 coronavirus-related deaths.
Prime Minister Boris Johnson warned cases could rise even more this week, as most legal restrictions have ended in England.
His spokesman said that the app was doing "what it's designed to do".
"We're aware of the impact on some industries and services and working closely with them particularly food and supermarkets….we have a robust and resilient food supply chain."
But supermarkets have warned they may have product shortages due to staff self-isolating.
The Co-op said it was "running low on some products", while Iceland said shops might have to be shut.
However, Iceland urged shoppers not to panic buy, saying it was not necessary.
Meanwhile, dozens of councils have suspended bin collections due to staff shortages from isolation and fuel provider BP has temporarily closed "a handful of sites" due to Covid staff absences.