login for users sometimes not working

Good morning,

I hope someone can point me in the right direction. I manage a website for a client who have a small online school. They use learndash and woocommerce. Now they have a few students who are just unable to log in. We have tried giving them new passwords and they just don’t work. I have checked. But other people have no trouble at all logging in.

That is why I can’t figure out what is wrong. If it is a plugin interfearing I would expect all to work or not work. Any idea in which direction to look and what to fix?

Best wishes,

Mieke Haveman