I guess the information hasn't percolated over here from the Bolt forum yet, but users have figured out the instability issue boils down to the BMS being unable to balance some poorly-binned cells that float up to 4.25-4.30 volts or more during charge. At those levels, it's only a matter of time before the separators break down and catch fire. So the failure mechanism is well understood; the root cause is basically one of these things: the BMS algorithm over-optimizes cell voltages at low SOC, it under-optimizes them at high-SOC, both, or some cars just have extremely high variance in cells and the BMS doesn't have enough balance current to even it out. Perhaps, also, the BMS doesn't cut off charging when the highest cell groups exceed the overvoltage threshold.
Some users reported 80-200 mV of delta at nearly full charge - pretty bad. Note that this is different from a Leaf with 130-150 mV delta when at low SoC.
I'm told it's easy to check cell balance with the app, so as long as you know your battery isn't one of the tiny number with an inconsistent pack, you should be in the clear - particularly with the GM "temporary" fix charge threshold of 4.0-4.1 V. There's speculation that the limit is at 95%, not 90%, but nobody seems able to tell the difference.
It appears that everyone's waiting for GM to decide on a permanent fix. Could be a BMS firmware patch (might not be possible over CAN), hardware intervention e.g. pack swap (extremely costly), full fleet buyback (might be less costly in 5-10 years with depreciation), or the permanent 90% hobble (which is essentially free).