Patients were waiting an average of 11 weeks for routine treatment at the Northern Lincolnshire and Goole Trust in January, figures show.
The Nuffield Trust think tank said thousands of patients on the waiting list across England are suffering in pain, while NHS staff are still dealing with burnout from the last two years.
NHS England figures show the median waiting time for non-urgent elective operations or treatment at Northern Lincolnshire and Goole NHS Foundation Trust was 11 weeks at the end of January – the same wait as in December.
This was shorter than the average 13-week wait a year previously.
There were 30,568 patients on the waiting list in January – up from 30,496 in December, and 28,104 in January 2021.
Of those, 342 had been waiting for longer than two years.
Nationally, 6.1 million people were waiting to start treatment at the end of January.
Health Secretary Sajid Javid recently announced NHS reforms, which include paying for patients who have been waiting the longest to travel to less busy hospitals or private facilities for care.
But Siva Anandaciva, chief analyst at the King’s Fund health think tank, said these promises will "ring hollow if hospitals throughout England continue to flash red".
He added: "Staff shortages remain the rate-limiting factor in the Government’s ambition to reduce the backlog.
"Without a fully-funded workforce plan, key targets will continue to be missed and people will continue wait longer for the care they need."
Separate figures show 1.5 million patients in England were waiting for a key diagnostic test in January – a rise on 1.4 million in December.
At the Northern Lincolnshire and Goole Trust, 15,379 patients were waiting for one of 15 standard tests, such as an MRI scan, non-obstetric ultrasound or gastroscopy at this time.
Of them, 4,176 (27%) had been waiting for at least six weeks.
The Nuffield Trust said the latest national figures on the state of the NHS make for "sobering reading", particularly amid a rise in hospital admissions for Covid-19.
Sarah Scobie, deputy director of research at the think tank, said: “Behind all of these figures are thousands of individual stories of pain and suffering, set against a backdrop of burnt out and overworked healthcare staff.
"The question for the Government is how far the reforms proposed will really touch the sides in the face of such long and growing waiting times.
"A renewed wave of the virus just as health and social care services are struggling to get back on their feet could be perilous for any hopes of recovery.”
Other figures from NHS England show that of 67 patients urgently referred at the Northern Lincolnshire and Goole Trust in January, 38 received cancer treatment within two months.
A month previously – when 77 patients were referred – 48 were treated within 62 days.
In January 2021, 57 patients were treated within this period, out of 80 that were referred.
The Department of Health and Social Care said its plan to tackle the Covid-19 backlog is backed by a multi-billion pound investment over the next three years, and it will also publish a 10-Year Plan on cancer.
A spokeswoman added: “We will deliver new surgical hubs and at least 100 community diagnostic centres to help patients get the surgery they need and earlier access to tests – including for cancer – delivering an extra nine million scans, checks and procedures by 2025.”