Auckland Transport spokesman Mark Hannan said there were 1.5 million transactions in November alone.
"In the previous six months, Auckland Transport received 772 complaints, a rate of .00495 per activated card."
The rollout was progressing according to plan but Auckland Transport acknowledged customers may have experienced technical issues, which were "inevitable with a project of this scale and complexity", Hannan said. "We would like to thank our customers for their patience and support."
Hop card overcharging delays 'frustrating'
Andy McCulloch estimates he and his fiancee have been overcharged at least 25 times since AT Hop cards went live on Birkenhead Transport buses in July.
"I think the concept of [integrated ticketing] is awesome, it's just got to work," McCulloch said.
The pair should pay $4.05 for each journey to and from downtown Auckland, but have been overcharged up to $6.
Overcharged fares were eventually repaid, but it was time consuming - the Beach Haven banker still has three reimbursements outstanding.
"I check it all the time now, it's pretty frustrating."
Auckland Transport spokesman Mark Hannan said there was an "intermittent technical issue" on Birkenhead Transport buses, and issues withinternet connections in Birkenhead in November.