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More than 96,000 people tested in England were unable to enter their results - meaning thousands of others risk not being notified of their proximity to positive cases.
The NHS Test and Trace website has an update which says developers are solve the teething problems "as soon as possible".
Many are also finding out that they cannot share their result with the app for England and Wales if they tested negative.
The app currently asks for a code to register a test result - but the code is only received if the test is positive.
It comes as coronavirus cases have jumped 60 per cent in a week to nearly 10,000 infections a day.
New figures from the Office for National Statistics shows there were around 9,600 new Covid infections per day in England - up on 6,000 last week .
During the last week the ONS said that there were approximately 1.75 new Covid-19 infections for every 10,000 people per day in the community - equating to 9,600 new cases per day.
The ONS stated that around 103,600 people within the community in England had the virus in the last week, this equates to around 1 in 500 people.
The ONS stated: "There is evidence of higher infection rates in the North West, Yorkshire and the Humber, London and North East; both West and East Midlands are recently showing a small increase."
Regional trends show that both the West and East Midlands are also showing small increases in case numbers.
In recent weeks the virus has been increasing across the country, and data from the ONS states that it is also increase in younger age groups such as the 17-24 group.
The ONS said this is based on "statistical modelling of nose and throat swab test results".
"In the data used to produce these estimates, the number of people sampled in some age groups who tested positive for Covid-19 is lower relative to England overall.
"This means there is a higher degree of uncertainty in estimates for some age groups over this period, as indicated by larger credible intervals."
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