Something doesn't add up on the FDR trace.
I've fine-pencilled / ruler'ed it. The first event appears to be the uptrim on #1, at 2:52:34. Increase in FF, ITT and Obj Tq. Once the Obj Tq on #1 reaches 100%, at 2:52:37 there seems to be a simultaneous Master Warning #2 Flameout, start of rise in Beta 2 (feathering), and a simultaneous drop in all #2 parameters, except the FF, ITT, NL and NH, which drop then stabilise (presumably at idle?) - so no ACTUAL 'flameout'.
The #2 looks like it didn't autofeather until 3 seconds AFTER the uptrim on #1 - and there doesn't seem to be anything in the trace that precipitates the #2 autofeather?
Shortly after that, #1 throttle is retarded about 10 deg. Not unusual I would suggest if they were having directional control problems. However, it is then progressively retarded (and at one point, the #2 throttle firewalled?) until the Fuel Shut Off is activated at approx. 53:15:22. Unlike the #2, the flame DOES go out in #1.
#2 turbine is running throughout.
In the last few seconds, it looks like #2 starts to unfeather (increase in Beta) - this seems to coincide with the #2 throttle being pulled back. #1 stays feathered throughout, although appears to relight as soon as the Fuel Shut Off is cancelled.
Seems like an odd sequence of events to me?