Possible reasons for a kafka consumer group to disappear?

[nc-ruth]

Hi all,

We have experienced a few times that a few of our consumer groups had their offset reset to 0.

Yesteday we experienced the same issue, but noticed that a consumer group disappeared (was deleted), and short after it got created (with an offset of 0). The disappearance happend exactly when 2 brokers was unavailable out of 5.

What could trigger this kind of behavior?
offset.retention.minutes is set to a year.