Strange Obsidian sync issue

Since October last year I've been getting into using Obsidian. Not that heavily, not to the extent some people do, but just as a way to keep a daily journal of work-related things. Each day at Textual HQ we finish off with a chat about how our day has gone, stuff we're wondering about, etc, etc... So I don't lose tack of what I've been up to I keep notes and Obsidian is how I do that.

One of the things I really like about it is how I can have iPhone, iPad and macOS versions on the go and have it all sync via iCloud. It generally works well.

But in the last couple of days I've noted the oddest problem, and I've yet to pin down the exact flow. But it seems to be this:

• If I create or edit a note on my iPhone, it doesn't turn up on my Mac.
• If I create or edit a note on my Mac, it turns up on my iPhone.

I think I might have seen variations on that theme but I've not made careful note -- normally I'm made aware of it when I'm trying to get something done.

What's super weird is this: on the iPhone, if I create a note, and then go into the Files app and look at the iCloud folders for Obsidian, the file isn't there! It's there in Obsidian itself, I can move it about, edit it, etc, etc... but it's not in the "vault" as seen from the Files app.

It's the last part that has be really puzzled.

If I get to the bottom of this I'll try and remember to write up what I find. I suspect I'm going to need some proper clear time, without other distractions, and experiment with all the edit and sync options and see what works and what fails.