'Victims let down'
The review also found officers prematurely closed some investigations on the basis that the victim did not support police action.
Police wrongly cancelled serious crime records
Inspector Zoe Billingham said she was "deeply troubled" by the frequency of closed cases without a full investigation.
"In too many of these cases, the force did not properly record evidence that the victim supported this decision," she said.
This was particularly evident in cases of domestic abuse, where seven in 10 were closed on this basis, Ms Billingham said.
She said it was "simply not good enough" that, despite being urged by the watchdog to improve in 2016, "concerns have not been addressed for over four years".
Ms Billingham did, however, acknowledge the force was taking action and had made a "marked improvement" in its recording of serious sexual offences and rapes.
A further inspection will take place in six months.