Presence of autocmd breaks asyncomplete

[emiel]

I failed to get asyncomplete working for the longest time. I was finally able to track down the culprit and have a vimrc (debug.vimrc below) file to reproduced the issue. The problem is an autocmd which appears to conflict with asyncomplete. I tested by checking for the presence of ~/asyncomplete.log. With the autocmd present asyncomplete does not start and the log file is not there. If i comment out the autocmd everything is fine and the log file is present.

The autocmd is something I copied a long time ago and honestly I don't even know what it does any more (shame on me). I've removed it from my config but I am still curious what is going on here and was hoping something with more vim knowledge can shed some light on the situation. Perhaps it can save someone else the troubleshooting effort.

vim --version
VIM - Vi IMproved 9.0 (2022 Jun 28, compiled Aug 13 2022 18:35:05)
macOS version - arm64
Included patches: 1-200
Compiled by Homebrew

vim9script

# vim -u debug.vimrc

set verbose=9

plug#begin('~/.vim/plugged')
Plug 'prabirshrestha/asyncomplete.vim'
plug#end()

filetype plugin indent on

## The following autocmd breaks asyncomplete
autocmd BufEnter * {
    # Prevent other buffers replacing NERDTree in its window
    if bufname('#') =~ 'NERD_tree_\d\+' && bufname('%') !~ 'NERD_tree_\d\+' && winnr('$') > 1
        const buf = bufnr()
        buffer #
        normal! \<C-W>w
        buffer buf
    endif
}

g:asyncomplete_log_file = expand('~/asyncomplete.log')

imap <C-Space> <Plug>(asyncomplete_force_refresh)