QuickType capitalises words unnecessarily
While I can't provide an explanation as to why this is happening, if this is really bothering you I recommend resetting the keyboard dictionary.  This is the 'nuclear option' for keyboard problems but it looks like you've tried everything else already.

To do this, go to Settings -&gt; General -&gt; Reset and tap on “Reset Keyboard Dictionary”.  Be care you tap the correct link here because you can accidentally reset a bunch of other parts of your iPhone, including Network or the entire iPhone.  Confirm you want to reset the dictionary and it will be wiped back to the factory defaults.

This will erase any and all modifications you have made to the keyboard but it will not erase any shortcuts you created or contact list entry name/nicknames.