This appears to be a (new) bug.
It's been happening on & off for the last few weeks.
(Coincidentally, the Message Box Size bug seems to have been cured about the same time)
I have Shipping switched OFF in Accounts & Settings > Sales > Sales Form Content.
I have Shipping unchecked in Custom Form Styles > Content > Header.
I have Shipping unchecked in Invoice Edit > COG > Choose What You Can Use.
Yet, sometimes, the Shipping Fields appear.
As far as I can tell the behaviour is random. It happens on different PCs using different browsers - both before & after a cache clearout as well as incognito/private browsing modes.
The shipping fields can appear when viewing an old invoice on screen (in edit mode, I use a docx template so the fields won't carry through to the print/pdf invoice).
The shipping fields can appear when creating a new invoice (from scratch or from recurring template).
(*edit - happens most often when viewing a previously saved invoice ... maybe 50% of the time)
To remove, go to COG > Choose What You Can Use
You will most likely see that the Shipping checkbox is unchecked or has a grey tick.
Enable Shipping - you get a green tick.
Then disable again.