Any suggestions please...?
The only thing I can suggest is the resolution difference is different between desktop and server - inside desktop you are getting a 'representation' of what it will look like with added compression due to having to fit the formatting menus on the left of the viz canvas area.
To resolve this, have you tried playing around with the column width on desktop (i.e. drag them to make them a little bigger), and then seeing the effect when you publish it to server ? It can be a bit hit and miss, and its usually related to text box sizes, but its something to be aware of.
The issue is resolved by disabling the auto scaling for high DPI devices. You can change this settings by going to properties of the particular application.