Ann: Suspension of Operations at Nifty Copper Mine, page-228

Up until recent times, no tin from Renison went into China due to logistic problems. Yunnan international sold a large portion of their Australian company to Greentech (formerly L'sea Resources International Holdings Limitted) and needed an agreement to buy tin for China which is mentioned below (the change in logistics arose due to smelting capacity changes and other production strategies in China, including the Mianmar deliveries).
Greentech are primarily an investment company and rely on Yunnan for their technical ability.
The relationship between Yunnan and MLX, as you point out, has been solid but not at all times (there was a time, when Renison was not making money that a few but serious differences arose. These were sorted). However, maybe Yunnan is now not as comfortable with MLX. Also, they are business men as well and if an opportunity was to arise, why wouldn't they take advantage. A deal that involved getting 100% of Renison would have to be an attractive option (see last paragraph of the article below.

Greentech unit renews tin supply deal with Yunnan Tin subsidiary

Greentech Technology International Ltd. said Jan. 31 that its YT Parksong Australia Holding Pty. Ltd. unit renewed a tin supply deal with Yunnan Tin Co. Ltd. subsidiary Yunnan Tin Australia TDK Resources Pty. Ltd. for another three years.

YT Parksong is held by Yunnan Tin Hong Kong (Holding) Group Co., Ltd., which is 82%-owned by Greentech's Parksong Mining & Resource Recycling Ltd. unit and 18% by Yunnan Tin.

The original three-year deal between YT Parksong and Yunnan Tin Australia expired Jan. 31, while the new contract will last from Feb. 1 to Jan. 31, 2022.

The new deal covers the supply of between 2,400 and 6,000 wet tonnes of tin concentrates per annum, including monthly shipments of about 200 to 500 wet tonnes, from Greentech's Renison tin joint venture with Metals X Ltd. in Tasmania, Australia.

Pricing of tin concentrates will be based on the average London Metal Exchange cash settlement price of tin metal within a 45-day quotational period, and subject to relevant deductions, penalties and treatment charges.

The deal has an annual cap of HK$480 million for 2019, HK$633 million for 2020, HK$765 million for 2021 and HK$77 million for 2022.

Greentech said it will explore further investment opportunities with Yunnan Tin, which has the world's largest production and manufacturing base for tin metal.