17K + posts is too much to read to see if this is covered but I have an issue with mail on my iPhone 6+ that is driving me nuts.
When I draft a message, new or reply, after dealing with who the message is to, CC'd, BCC'd, when you click in the message body at the top or the message there is behaviour that is strange.
In my case I have a default signature in message that is 8 or 9 lines of text. So I click in the blank above the signature to start typing but then Mail hides all the lines of CC, BCC, subject, etc and when I start typing my reply the cursor has actually placed itself in the middle of my default signature. Since I have to pay a lot of attention to the keys I need to tough to avoid typos I am focussed on the keyboard and I've typed complete sentences before realizing the cursor was between my name and title and not where I touched in the email.
It's really a nuisance that should not happen