Why I can't follow more than 600 users on Instagram from Android device?
Instagram lifted the restriction on my account and now I'm able to follow more people from android. I did not contact them though but the restriction was auto lifted after few weeks.

There was a temporary restriction on the account for some unknown reason that is most probably only known to instagram tech team because I did not exceed their follow/unfollow or like/unlike limit.

During this period I found same complaints from other instagram users on internet.