Since the beginning of June 2019, Instagram has changed its algorithms. Now, the limits are very blurry. You can not follow more than 1000 people per day, unfollow 1000 per day, add 2000 likes per day, etc. There are no clear limits for the actions per hour and day. The limits are calculated by Instagram's robot for each account individually and absolutely unclear how it does that.
Since that changes we can see new errors:
First problem: I CANNOT UNFOLLOW!!!
Guys, it doesn't depend on me. The app can unfollow so many, how many it allows Instagram. If you see the message "Your session blocked", you must do a new login to get a new session. You can click on (menu / logout) and then login again. Do not start a new unfollow process right after new login. Wait a few hours. It will be good if you change your IP address. After this, start to unfollow by a few people per hour. It's very important. If you will receive the message "Your session blocked", then open Instagram and unfollow someone, then do a new login in the app and right after that try to unfollow someone via the Followers Assistant, you receive the next message from Instagram: