“I am entirely not worried about the election results being affected,” he said.

The December poll, the first district council election held under Beijing’s “patriots-only” governing rule, was briefly interrupted by the system failure in the electronic voter registration system which prevented ballot papers from being issued.

Lok said at the time that the hiccup was unexpected as the system had passed a three-tier certification, and insisted a 90-minute polling extension was necessary to allow voters who had headed home after learning about the glitch to cast their ballots as he made a teary apology to members of the public.

The election drew a record low turnout amid a widespread sense of voter apathy.

Senior Counsel Bernard Man, who chaired the investigation panel, on Friday said the central processing unit (CPU) of the register system became overloaded at 7.37pm on election day.

Polling stations started using the printed copy of the electoral roll to issue ballots under a contingency plan, and a 90-minute voting extension was arranged.

The investigation found the utilisation rate of the system server’s CPU had reached almost 100 per cent. The higher load was due to design issues with two programs of the system, which caused computation time to increase as polling went along.

Another design issue of the system caused some work requests to unnecessarily take up substantial server resources, creating problems with issuing paper ballots, Man said.

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The two program issues that led to the glitch involved design changes made by the Information Technology Management Division of the Registration and Electoral Office to meet the operational needs of the poll, he said.

“The technical team of the Registration and Electoral Office did not fully consider the loading that might be induced to the system during actual operation, and therefore did not conduct sufficient and comprehensive load testing,” Man said.

He said the team failed to adequately explain the details of the alterations – which it considered to be “minor” – and the possible impacts to the two upper tiers involved in certifying the system, namely an independent contractor and an expert advisory panel.

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Asked whether anyone in the technical team should be held accountable, Man said the investigation panel was only responsible for determining the cause of the glitch and making recommendations. Any issues of accountability would be handled by the executive branch under established procedures, he added.

Man said the interim report would not be made public as it included design details of the system and the release could have an adverse impact on its security.

The investigation also ruled out the possibility of an attack on the “closed” system as no records of external devices attempting to access the register were discovered.

Lok also revealed an error was made in calculating the number of voters and the turnout rate given right after the election. The total turnout was 1,195,331 voters, or 2,138 more than was previously announced, he said. The turnout rate has been revised from 27.54 per cent to 27.59 per cent.

He said the error was due to the manual calculation of paper ballots by electoral staff, following the failure of the electronic system.

“Given the larger number of polling stations and due to the tight time frame for publishing the voter turnout, there was an error in the calculation by the electoral staff concerned, and the number of electors who voted at dedicated polling stations was omitted from the calculation,” Lok said.

He was referring to polling stations set up in correctional facilities and police stations for voters being detained.

But he stressed that those omitted ballots had been sent to the main counting stations and included in the number of votes obtained by each candidate.

The interim report was submitted to Chief Executive John Lee Ka-chiu on Friday, and a full one is due within three months of the election.

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Secretary for Constitutional and Mainland Affairs Erick Tsang Kwok-wai said the commission would submit recommendations on improvements to the government.

Authorities would work with the commission and Registration and Electoral Office to study and implement the recommendations to ensure similar incidents would not happen again, he told local media.

“We want to reiterate that despite the incident, it did not prevent this district council election from being a success,” he said.

New People’s Party chairwoman Regina Ip Lau Suk-yee said the lack of a load test behind the system failure was “unsatisfactory and disappointing”.

“The responsibility to ensure adequate testing does not rest solely with the IT staff of the Registration and Electoral Office,” she said.

“The head of the Registration and Electoral Office, a very senior executive officer of directorate rank, as well as the Constitutional and Mainland Affairs Bureau officials responsible for setting up the electoral systems, all share responsibility for this failure.”

Stanley Ng Chau-pei, president of the Federation of Trade Unions, said that although the interim findings provided some explanations for the glitch, many details had yet to be explained, such as why the system was overloaded, what changes were made to it and how maintenance was conducted.

He urged the authorities to further look into the incident and handle accountability based on the findings.