Didn’t you have an odd barline at the start of a Percussion part the other week? Is this the same project? If so, what was the solution with the percussion part and could it give a clue as to this?
edit: it was a strangely fat systemic barline. Could this be the same? If so, fix in Engraving Options.
This is a different project, no overweight barlines here.
It seems to be exacerbated by exporting the PDF from Acrobat as a different page size. I had a Dorico file with a page size of 7x10.25, which I exported to PDF and then opened and re-exported from Acrobat as letter size (with big margins for the printer).
I changed the Dorico file to letter size with large margins so I just have to export once, and the PDF is better… but the little notch on the bracket is still there.