vim version: NVIM v0.4.0-430-g8698830cb
node version: v11.12.0
coc.nvim version: 0.0.61
term: xterm-256color
platform: linux

Can't fix, no way to detect screen scroll.
What do you mean by screen scroll?
Thanks for looking into it.
If it's not caused by scroll, please provide minimal vimrc to reproduce the problem.
@chemzqm Try adding https://github.com/jparise/vim-graphql.
Got the reason, it doesn't check global variable existance in syntax file.
let s:tags = '\%(' . join(g:graphql_javascript_tags, '\|') . '\)'
coc only load syntax files for highlight, so it throws.