Custom ROMs and rooted phones aren't supported by WhatsApp. There are too many variations in these customizations for us to maintain a working product. Furthermore, custom ROMs and rooting don't allow the WhatsApp security model to function as intended. If you're using a custom ROM or rooted phone, other apps might be able to read your messages despite the end-to end-encryption.
For the best WhatsApp experience, please use a stock ROM and remove root. Contact your phone's manufacturer for specific instructions on how to unroot.