Unfortunately, I didn't post anything during these days but today I got an email which was probably sent to all beta testers with this text.
We care about your privacy on Instagram, so we wanted to let you know about a technical issue we recently found and fixed. It impacted certain Instagram accounts, including yours, that were using unreleased versions of Instagram as part of the Instagram Android beta program. The issue affected some beta testers who had more than one Instagram account logged in on their device. For a few hours between June 4, 2018, and June 5, 2018, it caused some posts or stories published from one account to be posted to another account logged in on the same device. As a precaution, we encourage you to look at your profile and make sure any posts from June 4 and June 5 were shared from the intended account. Protecting your privacy is our top priority, and we're constantly working to prevent issues like this. We're very sorry this happened. Thank you for participating in the Android beta program and for your help improving the Instagram app for everyone. If you have any questions, please contact us at email@example.com . Thanks, The Instagram Team
Apparently, it looks like this email is a part of GDPR regulation which is relevant for EU users. According to which, Data processor (Instagram) has to notify users about possible security incidents within a 30 days period.
The email is saying that stories were published in another account of the same user so probably it is not a major incident.
In addition to that, there is a problem with the current Alpha version 126.96.36.199.33 - some stories are getting stuck and it is not possible to go forward or skip them. For me, it happened twice in the stories bar and also in the user story from recent likes page.
Did you get this email too???