Which one will native speakers say?

Hi,

Background:
From previous posts, I understand that the following 2 sentences are grammatically correct and have the same meaning.

Question:
In this post, could you please tell which sentence would be said or preferred by a native speaker?

Sentence1:
I solved the problem that the classes were not long enough.
Sentence2:
I solved the problem of the classes not being long enough.

Thanks