When I do some cleanup in my Twitter contacts on Crowdfire, I sometimes get a popup that requires me to re-authenticate on Twitter (which requires me to enter the password). Sometimes clicking once to unfollow a single user is enough to trigger the reauthentication.
In my experience, this happens when you are mistakenly unfollowing users which you recently followed (less than a week ago or even a couple of days). This makes sense, because it's not nice to unfollow users shortly after following them (it's rude enough to harm you too).
In particular, there seems to be a limit of about 500 such unfollows every multiple hours: once you've hit that limit, it doesn't matter at which rate you unfollow further users, you just have to wait some hours or a day before you can unfollow more (Crowdfire suggests to wait 24 hours).
Hitting the limit is easier if you use the nonFollowers tool. The tool shows oldest non-followers first and should filter out those you followed less than 7 days ago, but sometimes fails to do so, perhaps so you have someone to unfollow even when you've already unfollowed all/most old non-followers.
In contrast, unfollowing users you followed weeks or months ago is not a problem: you can easily unfollow thousands in a row (I tried with manual clicks).