First, I rely on lomapaseo's astute observation that metal to metal at differing RPM is causative of heat sufficient to melt the masses.
If the Blades were leaving the IPT, (obviously at some point they do), then things can go wrong that have disastrous consequences. First, to potentiate a Gas Path Reversal (The Drums loss of pressure due partial IPT blade failure) the Dynamic Seal at the IP needs to be compromised. Ongoing blade loss covers this, and as it proceeds, the IPC would reverse their Stress (not their direction) such that the IPT is now 'Driven', not Driving?? It is at this point the already worn Spline joint scrubs smoothe. Now the IPT has nothing to do but 'coast' down, the HPC has lost pressure from IPC, and it has ceased driving the HPT which speeds on burning fuel the EEC has not had time to halt as yet. Now the IPC, The HPC, and the LPC/LPT are done, they roll stop. The remainder of P30 blows past the Bladeless IPT, (First Bang). The Wheel overspeeds or not, but has sufficient energy to Disintegrate, having lost the Drive Arm due Friction Heat and possibly P30 blowout. The fact that There is no discolouration and very little damage evident in the LPT Drum. suggests that everything that disintegrated, Blades, Vanes, Disc, Platform, etc. was blown forward out the chasm created by the First Bang, the exit of the contents responsible for the second Bang.
Obviously conjecture here. The timetable wants more precision. (Or deletion).