Passcode not working for students

We have a regular passcode our students have been using to join meetings. Starting last week, which seemed to coincide this latest Zoom update, our students are struggling with the passcode.

They are entering it correctly, but it is not allowing SOME of them into the meeting. They are using the correct case. A few of them WERE able to get it after trying the passcode multiple times, while others missed the meeting entirely because it would not work for them. 

Any clues about what could be going on here, and how to alleviate this? It's a quite problematic to have students unable to join a regular call.