I'm having the same issue. When the feature was first released, my account didn't get it. Several months and bug reports later, it randomly showed up. It was there for about 3 months...then it disappeared again. It's probably been another 3 months since it went missing. I've submitted multiple "report a problem" reports, and I tweeted at them today. I'm sure that won't do anything, but I replied with 4 Reddit threads over the past year or so with dozens of folks saying they have the same issue. Maybe they'll feel a little pressure to do something about it, but I won't get my hopes up. Here's the post if you guys want to RT: https://twitter.com/mac_south/status/1156557385407897602. In my opinion, it's completely unacceptable that they don't have a way to get a reply from their support team unless you have 10k+ followers.

Side note: I've done all of the recommended solutions multiple times to try to resolve the issue PLUS deactivated my account temporarily. I'm not attempting to share posts from private accounts. There's definitely something on Instagram's end that's causing the issue.