Finally, Xinhua News Agency has a report & video on this... 
It mentions the recovery failure was a result of "an abnormal combustion" (aka 异常燃烧). Part of report as follows: (translated)
It mentions the recovery failure was a result of "an abnormal combustion" (aka 异常燃烧). Part of report as follows: (translated)
This mission also conducted a recovery test of the first-stage rocket. However, an abnormal combustion occurred during the process, preventing a soft landing on the recovery pad. The recovery test failed, and the specific cause is currently under further analysis and investigation.
Although this mission did not achieve the preset goal of recovering the first stage of the rocket, it tested the correctness and rationality of the overall testing, launch, and flight plan of the Zhuque-3 carrier rocket, as well as the compatibility of system interfaces. It also acquired key engineering data under the rocket's actual flight conditions, laying an important foundation for subsequent launch services and the reliable recovery and reuse of sub-stages.
It is reported that the research and development team will conduct a comprehensive review and technical close loop of the test process as soon as possible, make every effort to identify the cause of the failure, continuously optimize the recovery plan, and continue to promote reusability verification in subsequent missions.