I think I might be missing something that is causing the unexpected behavior. But you are saying this happens to a published Viz, but not when it is on Tableau Public. I am curious if you could attach a sample packaged workbook (.twbx) to the post so that I can attempt to recreate the unexpected rendering behavior.
I am curious if this happens in Tableau Server as well.
Hope this helps!
Apologies for not getting back to you quicker, I'd moved on to other things, just come back to Tableau work. Realised that I was being thick, I had not unticked the max size on the dashboard tab. All sorted now. Amazing what time away from a problem can do.