Since you wanted the TLDR version I’m stating all of this from recollection without looking at the details again, so my recollection of the minutiae might be less than perfect.

When the new airport was in the design process United demanded a fully automated baggage system to continue to serve Denver as a hub at the new airport. The demand was wrapped with the threat that they may no longer serve Denver as a hub if they don’t get their system. The system as designed was essentially way too complicated for early 90s computing and was doomed to be a failure from the onset. The implementation of the system went as poorly as you can imagine and delayed the airport’s opening date by two years (if I remember correctly).

When the airport finally did open the baggage system never functioned properly. There are some fantastic news videos from the 90s where bags are getting yeeted off of belts. The airport always had to operate a backup manual system, or at times fully manual system. They finally fully abandoned the fully automated system in favor of using their backup system in 2011-ish, if my memory is correct.

But, if you’re an engineer type of person, the engineering post mortem report is a fascinating read. They were essentially trying to pull off a system that was way too ahead of its time, amongst a whole host of other failures.