> But somehow this suggests to me that I might have been doing something wrong. I use vim+ultisnips+(your excellent vimtex) while you use neovim. Out of curiousity, do you specifically set your python provider for your neovim in your config?

Yes, I do. I use a dedicated virtual environment for neovim which I create with the following snippet; then I set the `g:python3_host_prog` accordingly [0].

    mkdir -p ~/.local/venvs/nvim
    python -m venv ~/.local/venvs/nvim
    source ~/.local/venvs/nvim/bin/activate
    pip install --upgrade pip
    pip install pynvim

[0]: https://github.com/lervag/dotnvim/blob/c3169dd18f4396258f83c...