'attack':4 'cyber':3 'cyber-attack':2 'outsid':1

Damage/malfunction due to the recent geomagnetic storm

'damage/malfunction':1 'due':2 'geomagnet':6 'recent':5 'storm':7

Insider sabotage (e.g. a disgruntled employee)

'disgruntl':5 'e.g':3 'employe':6 'insid':1 'sabotag':2

Intentionally shut down on government request for national security reasons

'govern':5 'intent':1 'nation':8 'reason':10 'request':6 'secur':9 'shut':2

Expiration of something based on a date/time

'base':4 'date/time':7 'expir':1 'someth':3

Intentionally shut down to avoid exposure to a discovered security vulnerability

'avoid':5 'discov':9 'exposur':6 'intent':1 'secur':10 'shut':2 'vulner':11

Anything weather-related (including space weather)

'anyth':1 'includ':5 'relat':4 'space':6 'weather':3,7 'weather-rel':2

Intentionally shut down in response to an actual security breach

'actual':8 'breach':10 'intent':1 'respons':5 'secur':9 'shut':2

Intentionally shut down additional services to help recover from an unintentional initial cause

'addit':4 'caus':13 'help':7 'initi':12 'intent':1 'recov':8 'servic':5 'shut':2 'unintent':11

Unintentional shut down of additional services when doing an intentional shutdown of some small selection of services

'addit':5 'intent':10 'select':15 'servic':6,17 'shut':2 'shutdown':11 'small':14 'unintent':1

Accidental (physical world involved, not only software)

'accident':1 'involv':4 'physic':2 'softwar':7 'world':3

'-4882':5 'accident':1 'manifest':2 'scp':4

'-4882':5 'intent':1 'manifest':2 'scp':4

Australia's second-largest mobile telecommunications provider, 

 recently experiences a nation-wide service outage, with mobile phone and internet access unavailable for all customers, causing major disruption to business, finance, public transportation, and other important services.

https://www.abc.net.au/news/2023-11-08/optus-outage-live-blog/103076996

Optus CEO Kelly Bayer Rosmarin says the company has not identifed the root cause of the outage affecting millions of Australians, while there is "no indication" it has been caused by a cyber attack. Follow live.

Live: Optus has not identified cause of major outage, 'will not rest' until services back online

I'll resolve all answers as we learn enough to rule them in or out, according to information published by reputable media sources, or otherwise to my judgement, or N/A answers that can't reasonably be ruled in or out by end of year.

Note that if a primary cause is identified, all other causes not known at that time will resolve NO - they will not remain open on the off chance that there were muliple causes not yet identified at the time the primary cause was identified.

Feel free to add answers that are more specific than existing answers. For example, I've already added "outside cyber-attack", but you might add "Cyber-attack by <entity>", and both can resolve YES if they're correct.