"Owning Manhattan" star Jade Shenker is raising serious questions over the death of her father Marc ... as she isn’t convinced cops are on the right track, TMZ has learned.

The Netflix star tells us she isn't buying the authorities' preliminary findings that her father's death appears to be natural and to not raise any concerns ... saying she’s in the process of ordering a private autopsy to take a closer look.

Hollywood Police in Florida confirm to TMZ that officers responded to a death investigation at Marc's residence on April 12th, around 10 AM local time.

According to cops, they initially saw no need to look further into Marc's death, telling us ... “The preliminary investigation suggests no foul play, and the death appears to be natural.”

Jade tells us she previously retained an attorney and filed court documents claiming her father lacked the mental capacity to make major decisions -- however, she tells us the situation only escalated from there, with her father becoming increasingly isolated over time.

Despite police saying there are no signs of foul play, Jade believes more answers are needed, and she’s hoping an independent autopsy will shed light on what really happened to her late father.

Jade Shenker is a luxury real estate agent who gained public attention through her appearance on the hit Netflix series ... spotlighting high-end brokers navigating New York City’s cutthroat property market.