"Im more than convinced, she didn't attend the class." What does this phrase mean here? I googled it too, but the effort went all in vain.
In this usage, "more than" indicates that whatever threshold would be required to "convince" the speaker has been exceeded, by such an amount that there is no uncertainty or equivocation.
Common examples of this usage:
- more than convinced / persuaded
- more than satisfied / happy
The phrase more than basically means very. For example, these two statements are more or less equivalent in meaning:
I will be more than willing to help you solve this problem.
I will be very willing to help you solve this problem.
So, here's how you can understand your original sentence:
I'm very convinced that she didn't attend the class.