I've recently upgraded from 7.1.1 to 7.4 and everything seems to have gone correctly. But

I only see the "Quick Reply:" field when accessing a topic.

I see all the topics in the "Forum List" and am even able to post, but the view of the topic is empty. I am able to browse the topics with "Previous Topic" and "Next Topic" but they are all empty...

Anyone got any ideas?

I solved it with switching to Threaded Mode and back to Flat Mode in my user preferences.

And aplying in control Panel fixed it for everyone.