Found a fix, my problem was as per Dconnect suggested. I recently updated my graphics drivers and followed tips from gaming forums to improve performance etc, I believe I have inadvertently changed DPI settings somewhere, but for the life of me I can't find where. I have a lot of additional font types installed and I run 4 monitors from 1080p to 4k, so scalings can issue for me.
How ever all is not lost, I have found how to correct DPI issues that I created in Evernote in Windows 10 with Multi Monitors (Windows 10 version 1809).
1. Locate Evernote's installation directory, mine was in "C:\Program Files (x86)\Evernote\Evernote\"
2. Locate & right click on evernote.exe, select the 'Compatibility' and press 'Change high DPI settings' - see attached picture
3. Under 'Program DPI' tick the check box 'Use this setting to fix scaling problems for this program instead of one in settings' - see attached picture
(*Note I haven't played with advance scaling settings yet so there may be a better way)
4. Under 'Use DPI that's set for my main display when', select 'I open this program' in the drop down list. - see attached picture
5. Restart Evernote - (*Note ensure Evernote is not running in the SystemTray)
This corrected the issue for me, it may not work for everyone but I hope it points people in the right direction so you can tweak it for your setup.