Error "Key not found"

[alepez]

Sometimes I get this error when opening a cpp file:

error caught in async handler 'chromatica_parse [{'rpc': 'chromatica_parse', 'filetype': 'cpp', 'buffer': <neovim.api.buffer.  Buffer object at 0x7fd205247780>, 'args': [ ... ], 'tu': <clang.cindex.TranslationUnit object at 0x7fd205249d68>, 'filename': '...', 'bufnr': 1, 'range': [1, 31], 'highlight_tick': 0, 'position': [1, 1], 'changedti ck': 4}]'
Traceback (most recent call last):
  File "/home/_/.vim/plugged/chromatica.nvim/rplugin/python3/chromatica/__init__.py", line 42, in parse
    self.__chromatica.parse(context)
  File "/home/_/.vim/plugged/chromatica.nvim/rplugin/python3/chromatica/chromatica.py", line 121, in parse
    self.highlight(context) # update highlight on entire file
  File "/home/_/.vim/plugged/chromatica.nvim/rplugin/python3/chromatica/chromatica.py", line 210, in highlight
    if highlight_tick != buffer.vars["highlight_tick"]: return
  File "/usr/local/lib/python3.4/dist-packages/neovim/api/common.py", line 81, in __getitem__
    return self._get(key)
  File "/usr/local/lib/python3.4/dist-packages/neovim/api/common.py", line 44, in request
    return self._session.request(name, self, *args, **kwargs)
  File "/usr/local/lib/python3.4/dist-packages/neovim/api/nvim.py", line 131, in request
    res = self._session.request(name, *args, **kwargs)
  File "/usr/local/lib/python3.4/dist-packages/neovim/msgpack_rpc/session.py", line 98, in request
    raise self.error_wrapper(err)
neovim.api.nvim.NvimError: b'Key not found'

I don't know why but... opening a file with ":e filename" always raise this error, while opening with ctrlp works as expected.