I think informed speculation is inevitable, and I post with that a given. The AD itself focuses on "restricted" restrictors. Coking and Carbon were identified. Now this might be a maintenance issue. If failure happens before scheduled work, it is not a maintenance issue, but a problem that escaped design or materials considerations, or specifying a part incorrectly. The important part of the first AD relates to the "return line"
This return line(s) had installed restrictors to control oil flow. These restrictors evidently pack up with combustion and heat byproducts that further restrict the flow of lubricating oil. If the flow "back" stops, the pump continues to supply oil, and the bearing compartment may fill with oil, to overwhelm the seals.
Whether this is what caused the oil fire and loss of IPT is not at all shown, but whether a cynic or an innocent, it provides a very convenient explanation for the entire kerfuffel. For two cents worth of Coke/Carbon, this engine failed, and all we need do is restrict the too big installed restrictors and perhaps pull out the light tube more often. Easy Peasy. Move along then? Were I RR, or all the players, this explanation allows everyone a big "relief". Perhaps a relief (oil) that should have been designed in earlier?
bear