I am using InDesign 15.1.1 to create several accessible, tagged PDFs.
 
I have tagged every paragraph style correctly under the export tags for PDF (Edit all export tags > show: PDF), and I have left any list items and table of contents items with the default ‘Automatic’ tag.
 
I am exporting as an interactive PDF with ‘Create tagged PDF’ checked. 
 
Then when viewing the PDF in Acrobat Pro DC, in the Tags pane I have selected ‘Apply role mapping to tags’. This should ensure that in the tags pane in Acrobat, all my original paragraph style names are displaying as the tags that I have created. But this is not happening. I am finding that some of the tags are role mapping correctly, while several other tags are appearing incorrectly role-mapped with their original paragraph style names in place instead of the tags that I had assigned to them in InDesign.

There seems to be no logic to this. This role mapping problem is occurring on every document I export as a tagged interactive PDF, no matter the size (i.e. from a small 12pp booklet to a large 125pp brochure). The only common characteristic is that the initial pages of the PDF have the tags correctly role mapped, but then as the document progresses some of the tags start to break down with their tags not appearing and instead their original paragraph style names are displayed. I have tried exporting the PDF from my another Mac and I get the same result.

Today I have discovered something interesting: if I export just a few pages at a time then the role mapping is working correctly. The problem seems to occur when I export the full document – InDesign does not seem to be able to export all the information correctly en masse.

Note: I have updated to InDesign 15.1.2 today and the problem is still occurring.