The British emergency number had a bad IT upgrade, back in the 80s, which resulted in emergencies never getting displayed, only error messages.
I think it was in the 90s that an aircraft crashed because an airport monitoring computer was so infected by malware that it was unable to alert the crew or ATC that the aircraft had a serious issue and needed to abort the takeoff.
Recently, Oracle updated Birmingham UK's government IT system. It is no longer functional. At all. At a cost of hundreds of millions. The local government went effectively bankrupt.
I, honestly, DO NOT CARE that you cannot prove software "correct". We need IT lemon laws that make this kind of a botch-up very very very expensive for software vendors to mess up on. When something is mission-critical,
It might deter vendors from supplying government, but I'm not sure how that can be a bad thing. It is better to have an inefficient system than a new iand shiny broken one.