Mail says "Downloading" an attachment, but it doesn't download anything

Regarding the 'dead' thread https://discussions.apple.com/thread/8515738?page=2

is there an answer now? This is really frustrating: Apple used to lead the way, now it is just seemingly gone down the microsoft way (sorry to say) and 'dazzles no more'.

Why has the very annoying issue of "Mail says "Downloading" an attachment, but it doesn't download anything" not been fixed?

Thanks.