I had a very similar experience once. It was actually I think just a buggy cache deployment by Adobe servers.     Try this: In Launch go to all your app extensions. Make any change like ad delay of +1 in some setting, then save changes. Now just remove the delay +1 to back to normal. Resave again.  ...

No setting in workspace itself...   what happens if you change your printer setup to portait?

Check your file -> print menu   See if that is setup now in portrait then try and change it.   The browser is typically controlled by Print setting setup so try changing it then try resending the report.

what if you try from an incognito window?

Great point Jen...   Sophie if you want to see if your base report is too big try doing a control p of the browser with dashbaord on it see what sort of scaling is required to make it fit.   That could help you scale width down to fit more in line with an A4/letter size.

You are using send file on schedule right?   The pcs you use are they using any VPN to access the scheduling reports? 

ok no worries this is good as part of troubleshooting... Know Im asking alot but, can you try from a different PC?   I suspect its your windows printer settings may have some sort of auto size command...   Be great to rule out any PC setting this way.

Can you try a different browser to send the email?

What language is your PC set to?   any way to make a screen grab of some of the weird areas?

what operating system and browser are you using to create the PDF and setup schedule?