I'm going to make a bold prediction based on what information we have right now and say that the cause of the blackout is an attempted coup, and most likely by sentient bug spirits. Im going to list my hypothesis based on the very limited information that is available, so if you don't like spoilers, don't read any further!
We know that the blackout event has to do with strange and dangerous astral energies, which are not uncommon where bug spirits roam. Supposedly, the podcasts (and potentially by extension, the blackout) will run throughout the month of June, which is 30 days long. An announced upcoming campaign book is called 30 Nights which along with Cutting Black are about ARES fight against bug spirits. The UCAS has declared martial law, this points to an existential crisis not just in ARES but throughout the country. We also know that the blackout extends all the way to at least Texas, so I don't know what to make of that. ShadowcastersNetwork mentioned that bug spirits are suppose to be a big part of 6E.