For ages (possibly eons) Vi users have been plagued by the disconnection
between the screen buffer and Vi registers. Well, apparently Vim users
have been enjoying this fix for many years. I finally gave in after
discovering this one in particular.
Plug 'roxma/vim-tmux-clipboard'
It needs the following added to ~/.tmux.conf as well:
# form vim/tmux d/y buffer sync
set -g focus-events