A garda gave a character reference for an alleged child sex abuser after gardaí and Tusla were accused of failing to take sufficient action following the initial criminal complaint.
The matter came to light when the Garda Síochána Ombudsman Commission (Gsoc) carried out inquiries into how gardaí and the child and family agency Tusla handled the alleged sex abuse of a minor.
The issue of gardaí providing references in a private capacity was one of a number of policy issues raised by the Garda Ombudsman in its annual report for 2019.
During one investigation it was established that a serving garda member had provided a character reference in support of the defendant during his trial.
Gsoc said in its report that "given the nature of the allegations, the Commission considers it is not appropriate for Garda members to provide such references in a private capacity" and that they "could be perceived in a negative light by the public".
The oversight body recommended that gardaí should be issued with guidance on character references and they were informed that instructions are already in existence for this under the Garda Síochána Act.
Another garda was disciplined after sending drunk messages and an inappropriate picture of himself to a female after she reported a matter to him.
The woman had given the garda her phone number after he had taken a complaint from her regarding a family member, but in the following days she was sent "flirtatious and inappropriate messages" from him.
The report said he "alluded to her that he had done so under the influence of alcohol" and that the "garda later sent an inappropriate photograph of himself to the woman on social media".
The Garda Ombudsman found that there was insufficient contact to suggest a criminal offence was committed and a non-criminal investigation was launched.
He later admitted sending the messages and said that it was an error in judgment, and he was later fined for discreditable conduct.
As part of a separate investigation, a garda was sanctioned after being accused of failing to investigate the alleged grooming of a child by a relative in a timely manner.
They were among 1,896 complaints containing 2,280 allegations closed by the Garda Ombudsman in 2019, with 96 resulting in disciplinary action and eight criminal proceedings being launched.
It means that just over 4pc of complaints closed by Gsoc last year resulted in a criminal action or internal sanction, with 1,334 discontinued due to a lack of proof.
There were also 44 public-interest investigations opened where Gsoc did not receive a complaint or referral but was made aware of an incident through media reports.
In one instance the Garda Ombudsman launched a probe on foot of media reports about a senior garda sending inappropriate text messages to a female member of staff.
"The Commission concluded that an investigation should be commenced in the public interest as it appeared a criminal offence may have been committed," the report stated, adding that an investigation is ongoing.
Commenting on the report, Justice Minister Charlie Flanagan said: "The Garda Síochána Ombudsman Commission, along with the other policing oversight organisations, the Policing Authority and the Garda Síochána Inspectorate, carry out a very important oversight role.
"This is critical to public confidence in the service at all times, but none more so than at present, when An Garda Síochána plays such a central role in the national effort to tackle the Covid-19 pandemic."