I constantly change settings to A4 paper size, and constantly find that LO wants to use US Letter format. There must be a simple setting somewhere that deals with this? I have made what I think are the usual changes which seem to be persistent, but paper size constantly reverts.
I have made what I think are the usual changes which seem to be persistent
… and we should guess what you think the usual changes, which seem to be persistent, are?
If you are on Linux, you might want to read this FAQ. Otherwise, setting your LibreOffice locale to one that uses A4 should be enough; setting a custom default template is also an option. But - you didn’t mention neither your OS, not LibreOffice version, nor where exactly do you have to change the format: is that new documents that you create, or documents you receive from others?
… and as I keep thinking about it, I see more omissions: is this about page size used in documents, or about printer paper size? Is it about documents created in some specific way - like using New context menu in Windows Explorer? It’s very hard to guess when there’s no information at all.
Some OSes allow you to define default configuration for the printer driver. Unless you have changed LO options in some persistent way overriding OS defaults, LO retrieves the general page properties from the OS (active printer).
So, changing your OS default is alos a lead.