What are the issues with Solana?

I'm curious about Solana, the cryptocurrency. Could you elaborate on some of the key challenges it faces? I've heard about scalability and network congestion issues, but I'd like a deeper understanding. How does Solana's Proof-of-History mechanism affect its overall performance? And are there any security concerns surrounding this blockchain? Also, I'm interested in knowing about the competition in the market and how Solana stands out or lags behind its peers. Could you please provide some insights into these matters?