My guess is they threw out the chrono timeline code, and by the time they realized that was stupid, all of the coders who wrote it originally were gone, and they had zero documentation on prior versions, because most companies aren't far-sighted enough to take into account retaining legacy info/data
What is there to 'work' on exactly? From a programming perspective, this is trivial. Just put posts on the timeline from the accounts you follow in the order they were uploaded. Extremely simple. Its this current thing they're doing now that can have some work involved, as there's obviously various things at play.
Too bad that I don't use social networks like that anymore. I deleted all the apps, will redownload if I need to check something important and delete again.
"We made the instagram feed really ****** for the past 5 years, but now we are going to introduce you to the way it used to be, you know, before we made it ****** 5 years ago."