I switched to Joplin at the start of the week. Everything syncs fine but for one file. I can see it listed on my iPhone but there is nothing in the text box. I panicked and thought I'd deleted it but I can see it in Joplin on my Mac.
Thanks Ajay -- my problem is solved now. It was me being an idiot and not realising that I was looking at a notebook with a single note in it. I double-clicked the note and all is well.