Scene Action now in different placing on page in Scrivener 3? Why?

In Scriptwriting mode (UK script) the Scene Action used to be in the middle of the page not at the beginning of the paragraph. Although it is different from Scene Heading which is in BOLD it still seems strange to have it begin at the first tab rather than in the middle. Is there a reason this has been changed from Scrivener 2? And is there a way of changing this back to my preferred placing?

I don’t recall specifically, but we did make some changes to this preset to modernise it and bring it up to standards, in response to feedback from users. If you really want to revert back to the older script you could fire up a copy of 2.9, create a throwaway project using the stage play template, and from its Script Settings panel, first change the name at the top (something like “Stage Play UK (old)”), and then use the Manage… button to “Save for use in other projects”.

Now switch back to your v3 project, and from the Format ▸ Scriptwriting ▸ submenu, select the preset you saved. This will offer to convert the existing script material to the new settings, which you should do. I’d recommend creating a backup first, with File ▸ Save ▸ Back Up To…, just in case the conversion goes awry.

Refer to §19.7.1, Managing Scripts, pg. 490 in the user manual PDF for instructions on working with script presets (they are the same for v2.9). You might also want to create your own variant of the project template. See §5.4.4, Revising Templates, pg. 84, for instructions.