QWEEDDYZ: But did new saves working \sandbox itself?
And no. This one case is differ. First 726 been broken. This time it is players fault they keep playing it.
Even if im wrong about... but how im be wrong? Saves compatibility is optional feature of updates. Always been. Its not mine opinion. If some release\update release announce it is compatible - it shoudl be compatible. if devs didnt make such announce - they decide to not make saves backward compatible - they are not. So question is where to read official update changelogs for that updates...
No offence, but how about "no".
726 was available for over 2 weeks (at launch, after that weekend 727 disaster and even when the game was already being sold at full price, which is not cheap at all). It's not wrong of a user to expect 726's saves (sandbox included) to work after an update without any explanation or apology.
You're right in that we were not graced with changelogs and, perhaps, the devs/gog will never address any more issues. That reflects on them. It's not wrong of a user to expect a 4 year old game to work. Don't patronize other users for that.
This was simply not a good GOG launch - neither from the devs (broken builds), nor GOG (changing discounts in the middle of the promo period).
And I'm pretty sure the AI is still somewhat broken (tired and fired staff sometimes won't leave rooms, guests can queue up a single reception desk despite others being completely free).
Maybe the devs want GOG users to have the same launch experience as STEAM users got back in 2018... Or maybe they never fixed any issues on STEAM either...