XMR-Stak 2.3.0 was released a few hours ago. It looks like the startup time is faster for both NVIDIA and AMD GPUs. There's also Windows UAC improvements and support for Monero's anti-ASIC Proof of Work change.
Previous config files will not work with version 2.3.0. Run XMR-Stak without any config files in the directory and answer the prompts. Config files will be created for you.
Review the changelog and download it from https://github.com/fireice-uk/xmr-stak/releases.