Floating window appears on auto_popup = 0
The floating window appears even though g:completion_enable_auto_popup = 0
On minimal config:
call plug#begin('~/.vim/plugged')
Plug 'neovim/nvim-lsp'
Plug 'haorenW1025/completion-nvim'
call plug#end()
autocmd BufEnter * lua require'completion'.on_attach()
set completeopt=menuone,noinsert,noselect
lua << END
require'nvim_lsp'.pyls.setup{on_attach=require'completion'.on_attach}
END
let g:completion_enable_auto_popup = 0
inoremap <silent><expr> <c-p> completion#trigger_completion()
inoremap <silent><expr> <c-n> completion#trigger_completion()
it looks like this:

On my config it looks like this:

I'm very sorry for the long wait. I've been too busy to do anything last couple of weeks or so. I'll start looking into it.
Okay so first of all what you're showing in your gif is signature help. If you want to disable that you should use g:completion_enable_auto_signature = 1, the weird behavior in your gif still need to fix though.
Oh, I thought that g:completion_enable_auto_popup was the master setting for any type of popup and and the others are only for setting the details.
I have further investigated and it appears that the option let loaded_matchparen = 1 causes the signature to disappear (blink).
auto_popup is only for popup of completion! Also thanks for the extra information, I can’t figure what went wrong this afternoon so you help me big time!
Hmm the issue still exist let loaded_matchparen = 0 and I'm kind of lost because it works fine on my full config, I copied almost every config about completion-nvim in my tested init.vim but the issue still occurs...
Interesting. So the very presence of this option somehow changes the neovim or nvim-lsp behavior. Which in turn affects completion-nvim.