The patient, who had a cognitive impairment, was in Falkirk Community Hospital when they gained access to washing-up detergent mistakenly left out in the staff kitchen.
When they later became unwell, hospital staff contacted the out-of-hours GP service before the patient was transferred to Forth Valley Royal Hospital.
But their condition deteriorated and the patient died a week later.
A relative raised a complaint with the health board in a bid to find out what happened, and the board commissioned a significant adverse event review (SAER).
But health bosses were unable to conclude with any certainty whether detergent was ingested and contributed to the patient's death.
The relative, referred to as C in documents, then complained to the SPSO about inaccuracies and inconsistencies in the review and clinical records.
But the SPSO said it was not possible from the evidence available to confirm whether the patient, identified as person A, had ingested detergent.
The watchdog found the review to be “open and transparent”, but noted there were “inconsistencies and inadequacies in the records”.
An investigation found the transfer from the community hospital to Forth Valley Royal Hospital was not formally documented.
The report said there was also a delay in staff completing both an incident report after the detergent incident and the SAER, and in responding to the relative's complaint.
All of the complaints were upheld by the ombudsman.
The report said: "C complained about the care of their late parent (A) at Falkirk Community Hospital.
"A had a cognitive impairment and gained access to washing-up detergent that had been mistakenly left out in the staff kitchen area.
"A subsequently became unwell and advice was sought from the out-of-hours GP service prior to eventual transfer to Forth Valley Royal Hospital where their condition deteriorated and they died the following week.
"We took independent clinical advice from a nursing adviser and a GP adviser.
"It was not possible from the evidence available and advice obtained for us to confirm whether A ingested detergent.
"The initial advice given by the GP was to monitor A, when the observations should have prompted medical review.
"The GP assumed these observations were incorrect.
"When the GP later advised transfer to hospital, this was left to nursing staff to arrange and clear advice was not provided surrounding the urgency of the ambulance request.
"We found that the GP deviated from standard practice and failed to provide appropriate care to A."
NHS Forth Valley were ordered to apologise to the patient's family for all the “unreasonable' delays, failings in the system and failure to provide appropriate care”.
A spokesperson for NHS Forth Valley said: "We have apologised to the family and can confirm that NHS Forth Valley has taken action to address all of the recommendations highlighted in the report.
"We have also made a number of additional changes to further improve our arrangements for carrying out clinical reviews and strengthen our documents management and record keeping systems."