Ian,
Unfortunately the ACARS logs are 'under wraps'. Aside from the fuel load on board at 17:07, the absence or presence of a log off is also vital data in regards to the sequential timeline. This is under the purview of the criminal investigation, which is still open and ongoing.
I tend to believe that those 'early' reports vis a vis ACARS retain credibility.
If ACARS was tidily switched off, we then are almost certainly faced with an hostile act, either by crew or interloper. This is not pleasant to contemplate, but contemplate we must.
Along these lines (and I am in no way casting blame), the redundant FL350 transmissions AND the failure to read back the Ho Chi Min frequency loom much larger as true outliers, IMO.