Incomplete loading of Emails

I frequently have a error message saying that Email has not been competly loaded …
Parameters says : always completed load Email (translation from french error messages)
I don’t understand why

Is this error message show up when performing a search?  I believe eM Client does not downland the email until you open it, even if the “Download messages for offline use” is checked.  But when the search results are returned there should be a box that pops up allowing immediate download.