I had 20 minutes to solve 3 code reviews of react components. I was shown a code and had to find bugs and performance issues. But i didn't see the code working, it didn't have a description to it. I think this not enough time to complete a code review. I had 30 minutes to solve some challenges, i only finish 1 of them. It consisted in a description and a simple function that i had to complete. It was medium in difficulty.

Was okay. But looked like they were reading from a scripted document. Just read the question which was pasted in their dev environment. Explanation of the problem domain is not upfront given to you. You will have to grill them to get those as they just read the pated text again.