That's dishonest of the Guardian, at that time the government were only announcing hospital deaths and said as much at the briefings. Even now it's impossible to report all deaths day by day.
It was taking too long to collect in all the other sources, Care Homes, Private Homes, Hospices and elswhere, to be able to include them on anything like the same day, so they published the delayed numbers later in inclusive graphs and charts available online.
The staffs in the affected places were under extreme pressure at peak infection times and collating numbers and making returns were hardly a priority. As a result some returns were very late with weeks of delay before they were available to be included. The earlier the death, the more likely it would be subject to reporting delay with even some hospitals making very late returns originally.
Numbers weren't being hidden, below for example is London's proportions of all deaths by location up to the 5th of June. The reporting delays mean the latest date cannot be closer: