Error when rotate collectionViewController as contentController

[Arthur]

When rotate with opened side menu, there is an error with collectionView that's contentView.

Consider the following:

that's my collectionview with some items. Flow layout is applied, and items' width is equal to collection view width.
Thought it looks like this after rotation:

Have anybody faced this problem?

[Arthur]

Ok I figured it out. The solution is to get some delay before reloading collection view in viewWillTransitionToSize method.