STS - Speed Trim System.
There are times when the STS “appears” to run in reverse when it is functioning correctly, this can depend on what the pilot is trying to achieve and whether or not they are pushing or pulling...
The STS trims to try to return the aircraft the the “trimmed” speed.
Feel Diff Press light illuminating with an Airspeed Disagree and Alt Disagree sounds reasonable to me due to the elevator pitot input to the system.
as someone else mentioned, the airplane is in a depth that is easily reached so hopefully the DFDR is recovered soon and we will know more.....
RIP to those in the machine.