Non frequent users were disappeared

[eksigundem]

We have an application. Besides most of its features, if user permits the application, everday it sends a tweet that gives information about user’s daily followers, friends numbers.

But in the last 10 days we had a very big decrease. I give general numbers For example:

In 25 September 2015 we sent 5800 tweets for 5800 users,
26 September: 5800 tweets for 5800 users
27 September: 5850
28 September: 5800
29 September: 5500
30 September: 5100
1 October: 4600
2 October: 4100
3 October: 3900
4 October: 3900
5 October: 3950
6 October: 3950

As you can see from numbers, starting of 29th September we had a big lose and we want to understand the cause.
When application tries to reach user’s data it gets 401 error. It seems like user revoked application access. But these users use website for months, for years, so it is not possible for all of them to revoke on the same days.

When I contacted some of users, they say that they didn’t revoke access. When they check their Applications section, they can’t see our application there. It seems like our application is deleted from some of users. I suppose these users are not frequent users. For example a daily visitor doesn’t have this problem, but a non frequent user (for example user visits website once in a 3 months affected from this.

Can you give any clue for the cause ?
Did we reach a limit or what can be the reason ?

[eksigundem]

Regarding to this page, there exists 100k user token limit. http://thenextweb.com/dd/2012/09/05/twitter-releases-next-version-api-clarifies-user-token-limits-following-complaints/

It mentions this: “The 100,000 user token limit applies only to the small set of clients replicating the core Twitter experience.”

Although our application doesn’t replicate core Twitter experience, can the problem is token limit ?
Can this limit takes place in 2-3 or days ?
Can we understand this issue from a REST API call or by checking current API call results ?

In 3 years, more than 600k users used our application. We didn’t have such an issue until 10 days ago.

I hope @andypiper helps us.

[eksigundem]

And another issue with this topic. In last 6-7 days some of our users has this issue:

They signin with their Twitter accounts into our application. They start to add/remove people. But in the middle of operation they get invalid token error.

For example user logins at 00:32, make some works and at 00:34 he/she gets invald token error. Then user again signins with his/her Twitter account at 00:35, system creates new tokens. Then in 00:38 same thing happens. Invalid tokens.

When we contact with these type of visitors, they confirm that they didn’t revoke access to application.

So how can this happen ?
Please help us.
Thank you.