As authorities tweak MIQ rules - allowing some desperate New Zealanders in Australia the chance to return home - fresh IT issues have stopped people in some visa categories from accessing the country.
National MP Erica Stanford said it was "heartbreaking and cruel" of the government to leave at least 187 migrants out in the cold, and the problem unresolved.
As of last month, Resident 2021 Visa holders and families of essential workers have needed to prove they have a visa before their MIQ booking can be completed.
However, Stanford said the IT system that communicates with Immigration New Zealand to verify visas does not work.
That means people cannot progress any further, once they get to the front of the MIQ lobby queue.
"These poor people who were really excited about seeing their families again for the first time in two and a half years get an error message," she said.
"I was dealing with one family whose 10-year-old daughter they hadn't seen in two years.
"They were 400 in the queue which means they would have got an MIQ room, they had all the visas to travel and then at the last minute they got this error message to say 'you're not verified in the system' even though they should have been. It's just heartbreaking."
Stanford said the government should have identified and fixed the problem when it first changed the system.
"Once again migrants are left at the bottom of the pile. They don't seem to care much about them. Now migrants have missed out on two or three room releases which is just adding even more stress, anxiety and pain to their lives," she said.
In a statement, Managed Isolation and Quarantine associate deputy secretary Andrew Milne said 20,000 people had been successfully verified via the system since the change was introduced in December.
However, he said a small percentage - at least 187 people who have the legal right to enter the country - could not be verified by the system.
The number of affected travellers could be higher, due to "data accuracy issues", he said.
"Currently there is no manual verification system and unfortunately, an unverified passenger cannot book an MIQ space. We are investigating the issue and actively seeking to resolve it as a matter of priority. Interim solutions are being worked through to help affected travellers."
Milne said the visa verification was added to ensure people have the authorisation to arrive in New Zealand before booking a room, and so that rooms are "optimally used."
"Previously people would be able to book rooms even without the right to enter New Zealand. If they failed to show up those rooms would not be occupied. It also helped us combat the issue of a small number of incidents where fake passport details were being used to book a room," he said.
Earlier, MIQ said it had added two new emergency allocation categories for people stuck in Australia, after the planned border reopening was delayed.
People across the Tasman who were barred from booking MIQ rooms in March and April may now be able to return if they can prove they will face significant financial hardship, homelessness or unsafe living conditions if they stay in Australia beyond the end of February.
Applications will be accepted between 13 January and 13 February for people who can travel within two weeks.
Milne said MIQ understood how difficult it had been for New Zealanders who are desperate to return.
"This new temporary category will give them another way to get back home," he said.
Those who can apply for the new emergency allocation categories include people selling their house or finishing their lease, resigning from their job, or accepting employment in New Zealand which cannot be delayed.
MIQ said it was working with airlines in relation to future releases.