Now, assuming that ACARS remained switched off, what was the nature of the signals the satellite picked up until 08.11hrs local?
The satcom was active and linking to INMARSAT until 8:11am. ACARS uses the satcom to send messages (automated or manual) to the company, Rolls Royce, or Boeing- depending.
Both the ATC transponder and the ACARS *link* to the satcom were manually interrupted at different times. The ACARS would have attempted to send a message (perhaps an automated position report) to the company or Boeing, but someone disabled its ability to do so.
The only way to do that would be to pull the ACARS c/b or disable the SAT link via a sub-menu through an FMS CDU.