More than a quarter of transfers to and from the site are overnight, a watchdog says.
Just two out of 10 reports on an individual's suicide risk in 2025 led to release, data suggests.
A watchdog found some 60% of women held at the site were ultimately given alternatives to detention.
Campaigner Dr Helen Groom says the figures prove many women are being held unnecessarily.
Better phone reception at the centre in Consett was dubbed a "priority" years ago, a watchdog says.
Campaigners say women are kept at the site indefinitely and describe the practice as "cruel".
Campaigners say the County Durham facility for women waiting to be deported causes distress.
Inspectors made a surprise visit to the centre which opened amid protests in 2021.
Campaigners say the women at the centre were failed by the system - which the government denies.
