Another agent, based in Turkey, was now waiting for instructions for the cargo. He said: "We don't know what will happen."
The agents did not disclose who owned the cargo.
The UN has stressed it is common for cargoes to change hands while en route. However, the failure of the closely watched vessel to complete its journey highlights the challenges international organisations and grain traders face in trying to alleviate the growing food crisis and normalise trading in commodities markets.
The rejection of the Razoni's cargo also raises questions over the condition of the grain which had been loaded on to the boats in the Ukrainian ports when Russia started its invasion of Ukraine in February.
The UN-led Joint Coordination Centre (JCC) said its inspectors checked whether the vessel, which left Odesa on August 1, had any unauthorised crew or cargo on board. "We are not involved in conducting food inspection. This is not part of the agreement," it said.
A total of 12 vessels carrying more than 370,000 tonnes of food commodities, including corn, sunflower meal and oil, have left the Ukrainian ports of Odesa, Chornomorsk and Pivdennyi.
None of the ships are covered by the Lloyd's consortium that agreed to cover the cargo on the vessels operating under the UN-brokered agreement, although insurers believe they have some liability cover. They have been keenly watched by insurance companies to assess whether coverage of further exports is viable.
"Details about quality control are understandably vague but the Razoni's cargo was rejected by the buyer in Lebanon so there will likely be some further problems particularly on the older grain which should be seen as distressed cargo," said Neil Roberts, head of marine and aviation at the Lloyd's Market Association.
"For now, the good news is that some vessels are out and some grain export has resumed but much remains in the balance."
While the aim of the grain corridor agreement is to reduce food insecurity round the world and contribute to the prevention of global hunger by facilitating exports of Ukrainian grain and fertiliser, the JCC said it was prioritising the departure of vessels that were ready to leave Ukraine to free space for inbound vessels and help clear grain silos.
Two vessels have arrived in Ukrainian waters this week, although there are no others scheduled at this point, according to shipping platform Sea.
The JCC said it was too early to assess the impact on global food markets of the reopening of the Black Sea. When operations are full and running, exports could reach 2 million to 5 million tonnes for the duration of the initiative, which runs for 120 days, it said.
"All parties at the JCC have recognised that this is a humanitarian initiative and they are working towards that goal," it said. "At the same time, though, we will not be able to control the commercial world."
-By Emiko Terazono and Ian Smith in London, Samer Al-Atrush in Dubai
© 2022 The Financial Times Ltd.