Upon further reading I found that the Viability Event (which is also a Write-down Event) is probably the applicable one in this case:
> (b) customary measures to improve CSG’s capital adequacy being at the time inadequate or unfeasible, CSG has received an irrevocable commitment of extraordinary support from the Public Sector (beyond customary transactions and arrangements in the ordinary course) that has, or imminently will have, the effect of improving CSG’s capital adequacy and without which, in the determination of the Regulator, CSG would have become insolvent, bankrupt, unable to pay a material part of its debts as they fall due or unable to carry on its business.
Clearly this deal required non-customary, extraordinary support from the Public Sector, so if the regulator determines that without such a transaction CSG would have liquidity issues, then this event would occur.
However I think my point stands that the terms of these CS AT1 notes should be understood as materially different from similar securities. For example, this note from ING (https://www.ing.com/MediaEditPage/XS2122174415-ING-Groep-N.V...) has a single Trigger Event that will cause mandatory conversion into ordinary shares, and a more general provision for Statutory Loss Absorption which may be a conversion or a write-down. The terms of CS AT1 notes do not seem to provide for any automatic or discretionary conversion, only automatic write-down.
I completely agree that in situations like this, the regulators have a lot of discretion on these bail-in securities, but I consider this "automatic permanent write-down" feature to be of a materially higher risk than "automatic mandatory conversion" variant because it could be a difference between getting back something (or everything) vs nothing. What the regulators do are, by definition, not "automatic", and an automatic write-down should be a much lower hurdle than an explicit regulatory action.