The overall number of complaints about the Luas from passengers declined slightly last year - despite record numbers travelling on the light rail systems.
However, there were increases in reports about problems with ticket machines and the behaviour of Luas staff.
Figures published by the National Transport Authority show that Transdev, the operator of the Luas Red and Green lines, recorded a total of 5,190 complaints last year down from 5,207 in 2018 - an annual decrease of 0.3pc.
Complaints about disruption to services - the single biggest source of passenger grievances - were down 10pc to 1,868.
NTA figures show the reliability of services on the Red and Green Lines improved last year averaging 98pc - up from 97.3pc in 2018.
However, the number of complaints about issues with ticket machines has jumped by 45pc to 941.
The third biggest issue among tram passengers was staff behaviour, with an 8pc increase in complaints about the conduct of drivers, inspectors and security staff. Some 46 additional complaints, up from 613 last year, were received - the highest level in years.
The number of people claiming to have suffered personal injury while travelling on the service rose by 18pc to 210.
Complaints about overcrowding were down 38pc to 124, while reports of anti-social behaviour declined by 3.5pc to 419 - the lowest level since 2016.
The NTA figures also showed that Transdev is failing narrowly to meet its targets on punctuality - with the Red Line experiencing longer excess waiting times to scheduled departure times compared to the Green Line.
The Luas came into operation in 2004 and, with several of extensions, the network extends to 42.5km over two lines.
The light-rail system carried a total of 48.1 million passengers last year - its highest ever figure, representing an annual increase of 15pc.
A spokesperson for Transdev said the company always worked to ensure customers had a positive experience when on board.
"When something falls short of expectation and a complaint is made, we always investigate such complaints fully," the spokesperson said.
Transdev said Luas ticket machines recently underwent an update to improve the user experience for its customers.
"This along with the increase in Leap Card usage will greatly enhance the service," the spokesperson said.