The ombudsman said the council’s response to the complaint apologised for “poor level of service” and that the authority stated crews were given “additional reminders”.
But issues reportedly continued towards the end of 2024.
The watchdog said the council stated it was unable to comment on what “caused the missed collections as the driver and crew are involved in the industrial action”, but “it again suggests the later start times introduced in 2024 are a potential cause”.
The report stated a number of missed collections were eventually “closed”, meaning the council completed them later.
Addressing missed collections earlier this year, cabinet member for environment Majid Mahmood said: “We don’t want to see a single complaint coming through to customer services because of non-collection.
“No resident should have to go and pay for their own skip. It’s a service that we have to by law provide to residents.
“If there’s specific issues… that’s something that we need to intervene with.”
He added in January that new technology would make a positive difference and the system was being reviewed around tower blocks and maisonettes.
Mahmood has said changes to the city’s waste service will provide people “with a better waste collection service” in line with other councils.