neovim :checkhelath tells me to upgrade neovim-python-client to 0.3.0
checkhealth aside, there is problem with neovim-9999 (and soon other versions of neovim) and python. Since 0.3.1 (https://github.com/neovim/pynvim/commit/f2372385d1be6ed62ee458d5e017fff3541ce0f7) devs renamed python module. neovim-9999 (https://github.com/neovim/neovim/commit/3ea14d53664ca7dba648e650d4047e01a8518231) already looks for pynvim.
I can confirm this. I am using neovim-999