An investigation into complaints made against the former head of the UK’s oldest drama school has reported a “serious breakdown of relations” between her and some staff “due to weaknesses in communication, leadership and change management”.

Sarah Frankcom is departing as director of Lamda (the London Academy of Music and Dramatic Art) after 18 months in the job.

Her resignation was announced in August. At the same time, Lamda said it had received complaints about some aspects of her conduct and management style.

On Monday, Lamda published a lengthy statement in which it expressed support for Frankcom’s ambitions and actions in the job, but raised concern about the execution. Frankcom also released a statement in which she expressed pride at her achievements.

Frankcom joined Lamda with a mission, she said, “to make change, progress work on diversity and bring an industry relevant approach to training”.

One of her first moves as director of Lamda was to cut the cost of first-round audition fees to get into the school.

The Lamda board said it backed changes and restructuring that Frankcom led but added: “There must be a distinction made between the support for change, and support for the way in which change is implemented.”

In summary, the statement said: “The investigation found evidence of a serious breakdown of relations between the director and some staff over implementation due to weaknesses in communication, leadership and change management.

“The way in which change was managed was not always clear or inclusive.”

The inquiry found that Frankcom’s actions “were neither malicious nor intended to cause distress” and that events were made worse by the pandemic.

Frankcom is a respected figure in British theatre. Before joining Lamda, she spent 21 years at Manchester Royal Exchange, where she was sole artistic director from 2014.

She regularly collaborated with Maxine Peake, directing her in productions including Hamlet, Miss Julie, Happy Days and A Streetcar Named Desire. She also established the Bruntwood prize for playwriting, the biggest of its kind in the UK.

In her statement Frankcom said she had been Lamda’s director and its director of actor training. “I am stepping down because the situation of performing both roles has become untenable, both for the organisation and for my health.”

She added: “I am proud of what I have achieved and the care and due diligence that I afforded all students and staff during an unprecedented set of circumstances.

“I am human and whilst there are of course things that might have been handled better, I believe I have always worked in a transparent, collaborative and empathetic manner.”

Earlier this month Frankcom was supported by “an open letter to the board of Lamda in support of Sarah Frankcom”. Signatories included about 70 full-time and freelance Lamda staff as well as industry figures such as Peake and Michelle Terry, the artistic director of Shakespeare’s Globe.

The Lamda board’s statement said lessons would be learned and action taken “to ensure ongoing change is implemented in a fair and inclusive way”. It said Frankcom had indicated her intention to leave in May, well before complaints were received.

It concluded: “The board gives its sincerest thanks to Sarah for all her efforts during her tenure at Lamda and wishes her well with her future projects.”