Brandi Mallory died in a bizarre manner that, for now, remains a total mystery -- although one piece of the puzzle has been answered ... she died after a dinnertime food run.

TMZ has obtained the police report pertaining to the "Extreme Weight Loss" star's death -- and it's fairly shocking to see what cops say preceded her sudden passing. Per the Atlanta PD paperwork, Mallory was last seen alive while buying some grub from a local Chipotle.

The report notes that Mallory's vehicle was spotted in the parking lot of a strip mall early on Nov. 9 -- this while the owner of an adjacent deli noticed it just sitting there all by itself.

The deli owner told cops he also saw a female inside who appeared to be asleep -- but the alarm bells started ringing when he says he saw the car there much later in the day ... which signaled to him something was wrong. As it turns out, there was ... BM was found deceased.

The police report says cops reviewed surveillance footage that showed Mallory pulling into the lot the night prior around 5:53 PM ... at which point, she went into the Chipotle, came out with her food, and then went into her vehicle -- but never left or came out after that.

The cops note there's no sign of foul play, and her exact cause of death is still under investigation. We should note ... there's no evidence her Chipotle meal had anything to do with her death.