It's not at all unusual for the SAF option to disappear when there is disruption to your journey, or when it's a multi-modal trip like yours.
Originally Posted by
Timo Bossier
However, I always buy this a couple days out at max, when it’s as sure as can be the trip will be ‘on’. I’ve purchased as late as 1 hour before boarding recently.
The option to buy SAF should show up again during check in, or afterwards in the app after you have checked in.
In my (limited) experience of itineraries where the SAF option "disappears" between purchase and flying, it's always available as normal either during check-in, or after check-in when you consult your booking in the app.