The issues have been occurring since at least Wednesday last week.
It is not known how many vehicles have been affected.
Former deputy Mary Lowe, a regular bus user, said on social media that she had been on several services this week, sometimes more than one a day, and each time all passengers had ridden free of charge.
‘The bus card machines have been covered over for days now, resulting in loss of government revenue,’ she wrote.
She said there was still a problem on at least some services yesterday afternoon.
‘It’s been both small and big buses. There’s been a lot of people not paying,' she said.
Other bus users told the Guernsey Press that they had seen the issue on a few buses.
A Stagecoach spokesman said they were aware of a number of ticket machines on local buses which were currently affected by a technical issue.
‘This is linked to the Ticketer system used across the network. This is a supplier-related software issue, and we are working closely with Ticketer to help them resolve it as quickly as possible. We would like to thank our customers for their patience and understanding while Ticketer works to implement a fix,' he said.
Laura Oxburgh, head of on-island travel and transport implementation for the States, said the matter had been brought to their attention on Friday.
‘The bus provider, Stagecoach, has investigated the cause of this over the weekend and it is now understood they were the result of a software issue following an update administered by the system provider, Ticketer,’ she said.
‘Stagecoach are working with Ticketer to urgently resolve the matter.’
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