Why did the NZF president quit the party?

The Herald reports:

The president of New Zealand First has quit after just a year in the job – and the long-time member says he is walking away from the party altogether.
But it remains unclear why Lester Gray has decided to leave, after being elected at the party’s annual meeting this time last year.

Mr Gray had taken medical leave, and health issues would be a logical explanation for standing down as President.

But there is no way health issues would be why you are quitting as a party member. That strongly suggests there is more to this story that it seems.

The party president is the most senior volunteer in a party. To have a party president quit as a party member is unprecedented in my memory.

UPDATE: Stuff further reports:

NZ First party president Lester Gray has quit the party, citing his refusal to sign off financial reports for ‘moral’ reasons. 
A resignation letter reveals Gray took his stand against signing the party’s 2019 reports with a claim he has been kept in the dark over party expenditure and donations, leaving him unable to put his name to them with confidence.
The shock departure raises concerns about the internal financial arrangements of one of the government’s crucial coalition partners as election season looms in 2020.

It seems Lester Gray is an honest man.

NZ First have (off memory) never ever disclosed a donation. Yet everyone knows they get significant corporate donations from the industries they represent in Parliament – forestry, fisheries and racing.

The party office holders often get left in the dark, with Winston or his office or lawyers actually controlling the donations or money. A former party secretary filed numerous incorrect donation returns which she had to correct.

The Electoral Commission is charged with ensuring party’s donation returns are accurate. They should be talking to the former President to ascertain what his concerns were.