More than 3500 Scots who tested positive for Covid-19 have not been spoken to by coronavirus contact tracers.
And more than 9000 people who were contacts of someone with the disease were unable to be traced.
The figures emerged after a “coding error” was found to be responsible for overestimating the number of people contacted within 24 hours of testing positive for the virus.
Now the Scottish Government has said there are a “small minority of cases it has not been possible to reach”.
It said these individuals have not responded to “repeated attempts by the contact tracing service”.
Public Health Scotland figures show that since June 22 a total of 3512 people with a positive test were unable to be contacted by staff from the Test and Protect system.
The report said this was 6% of those who had tested positive, describing it as a “very small proportion” of the number of cases.
There were a further 9252 contacts of coronavirus patients were unable to be reached since June 22 – representing 4% of this group.
Labour health spokeswoman Monica Lennon said: “Thousands of people who tested positive have slipped through the net, as have thousands of their close contacts.”
She called for action from both First Minister Nicola Sturgeon and health secretary Jeane Freeman.
Lennon added: “The cabinet secretary and the First Minister need to cut out the spin and complacency. Fix Test and Protect for all our sakes.”
A Scottish Government spokeswoman said: “It is vital people engage with contact tracing teams whether they have been tested for Covid-19 or are identified as a contact.
“Anyone taking a test will be asked to provide their name and a contact phone number.
“Contact tracers will call and text this number three times over 24 hours and, if not reached, a message is left to call the contact tracing service back.
“In a small minority of cases it has not been possible to reach individuals who do not respond, despite repeated attempts by the contact tracing service.”
The spokeswoman added: “Our contact tracers have successfully interviewed 94% of people who have tested positive for coronavirus.
“In the week from November 2 to November 8, Test and Protect completed 95.8% of cases within 72 hours – far exceeding the World Health Organisation standard of 80%.”