The Land Transport Authority of Singapore has published the executive summary of its investigation into the rear end collision at Joo Koon station on 15 November 2017:
https://www.lta.gov.sg/data/apps/news/p ... Report.pdf
The five page summary does give an idea of how the accident happened, but the lack of detail means that the actual causes are obscure. I was surprised at the lack of detail in the report about the processes used to manage failure of the system. Unfortunately, the full report does not seem to be available.
This appears to be an internal investigation into the accident, not an external investigation as would occur in the UK, USA (or even Australia).