Restore in the wrong direction?
Reminds me of one occasion a few years back. Had installed an active-active firewall pair across two sites with each handling one leg of a 2MB leased-line to the internet (see, I said it was a few years back!) and automatic config hot-synchronized between the pair.
One firewall sends alarms to say fan playing up. No problem, will just power it down, replace with a good unit then bring it back up again. Power down the offending unit, traffic fails seamlessly over to the secondary and all good. Re-cable from dead unit to the new one, power up. Still all good. Give the "re-synch" command and hear someone outside wondering why the internet has stopped working. Upon closer inspection I determine that the re-synch has indeed happened, with the configuration being dutifully copied across - but I now have two units each with a blank config. Heart stopped and blood ran cold as I realise what I've done...
Fortunately it was only a 15 min sprint to the other site where I had a laptop with all the backed up configs. A lesson learned the hard way indeed!
But TBH in BA's case I can't believe that the Friday of a Bank Holiday weekend wasn't considered a change freeze with nobody allowed to do anything other than emergency work in their DCs.