Well, so far the system "solved" this by splitting the trip, so now it shows separate journeys from YYZ to LHR and from LHR to VIE (rather than one YYZ-LHR-VIE trip) on the website But I assume it at least means the system recognises that the connection isn't valid and hopefully something will be done about it automatically.

I also got another schedule change, this time concerning the outbound trip where LH flight got cancelled and I got rebooked. Apparantely LH's IT talks to AC better than BA's so this one is actually shown as a schedule change in the MMB. What's peculiar is that it wants me to acknowledge the change or pick another flight, but when I click on the link, it doesn't give me any such options. Furthermore, I'm now locked out of seat selection, flight changes and other features of MMB. Not too happy about this...

On the other hand, it now also says I'm eligible for a refund, despite the outbound flight change being fairly minor (I assume it's because it's technically a flight cancellation, not a schedule change). Can I rely on the information on the website, i.e. if it says I get 2700 eur refund, I will get it? I know it's a dumb question but I had bad experience with another airline in the past At this point I'm considering cancelling and booking again as it saves me the hassle of calling and I might rebook myself to travel via CDG instead since BA is no longer an option for the feeder flight and I don't fancy flying OS.