Instagram has a pretty craptastic UI itself. It's a pain in the ass to copy images from the web UI (Have to use the inspector to get the link) and the video player doesn't let you skip ahead or move back.
I'd agree if those tasks were part of what they were planning to be a part of the app experience - but seeing as they're explicitly not, then from a pure design perspective, the UI is perfect in that regard.
It's bad, but bad intentionally. I haven't noticed it being buggy like snap chat. They just went out of their way to break features the browser gives you for free.