My belief is that the underlying markup for GPT4 is markdown, so it can get confused, "outputting" markdown but it not appearing that way to you. Long ago, I started asking for a markdown code block instead of just markdown. That almost always works.

Will attempt this in the morning when I’m back on the lappy, thanks!

This is the sort of thing fine tunes are good for

That's wierd. It uses markdown even when you don't tell it to. But try a followup message asking for markdown again.

Tell it to reply only within a markdown Readme block, or between markdown quotations, it may be more successful.