Recently, when I forward an email, I get the You are attempting to forward an email without attachment. In some cases, I’m not aware there is an attachment, but in all cases, there is no option to include the attachment. I can say yes to send without or no to return to the send dialog.
I can’t find it right now, but I know there is a setting for a warning for missing an attachment. I think it searches for words like “attached”. So if that word is in the email you would get the warning.
And you can attach files to forwarded emails. Either click on the paperclip icon of click on Menu then insert, then File.