The Independent Police Complaints Commission (IPCC) said Jacqueline Oakes, of Birmingham, was let down by a raft of procedural errors and failings to identify the risk she faced.
She was battered to death in 2014.
The West Midlands force said it agreed with the findings on its employees.
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In all, the actions of 40 staff were examined by the IPCC - "one of the biggest investigations" it has carried out, it said.
The inquiry looked into 19 reported incidents involving Ms Oakes, 51, and her killer Marcus Musgrove in the run-up to her death at her home on 14 January 2014.
Musgrove was jailed for life that year.
Errors were made by officers and control room staff, the IPCC said.
Among the failures, the investigation found, were those of five detectives who did not ensure they were adequately informed before determining that Musgrove should be bailed.
On 10 January 2014, four days before she died, Ms Oakes gave a police statement about an incident in which Musgrove breached his bail conditions.
There was an outstanding warrant for Musgrove for the breach when she died.
The IPCC said it found there were at the time "significant organisational failings" in the way the force managed outstanding arrests of this type, which meant "arrest attempts" were not made until 12 January 2014.
Ms Oakes's daughter, Jenny, 36, said: "I will never be able to understand how such a slack attitude to a situation of potential escalating domestic abuse can be taken by so many people at a police force. It is shocking."
In addition to the 19 employees said to have a case to answer for misconduct, a now retired officer was found to have a case to answer for gross misconduct.
No misconduct was identified for a further 20 employees whose actions were investigated.
The IPCC said two officers would attend misconduct meetings, with others subjected to "management action to address the failings".
No action is to be taken against the retired officer.
Deputy Chief Constable Louisa Rolfe, of West Midlands Police, said: "We acknowledge that some of our officers and staff failed in their duty to complete certain checks, risk assessments and, on occasion, follow the force's domestic abuse policy and for this we sincerely apologise to the family of Jacqueline Oakes."
Nineteen police officers and staff have a case to answer for misconduct in their dealings with a domestic violence victim before her murder, a major investigation has found.