Patients were waiting an average of 17 weeks for routine treatment at United Lincolnshire Hospitals 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 United Lincolnshire Hospitals NHS Trust was 17 weeks at the end of January – up from 15 weeks in December.
This was also more than the average 16-week wait a year previously.
There were 61,219 patients on the waiting list in January – up from 59,740 in December, and 41,023 in January 2021.
Of those, 2,758 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 United Lincolnshire Hospitals Trust, 16,842 patients were waiting for one of 15 standard tests, such as an MRI scan, non-obstetric ultrasound or gastroscopy at this time.
Of them, 6,925 (41%) 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 show cancer patients at United Lincolnshire Hospitals Trust are not being seen quickly enough.
The NHS states 85% of cancer patients urgently referred by a GP should start treatment within 62 days.
But NHS England data shows just 40% of patients received cancer treatment within two months of an urgent referral at United Lincolnshire Hospitals Trust in January.
That was down from both 43% in December, and 62% in January 2021 last year.
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.”