Form fields tags aren't exporting properly for tagged pdfs in the newest Indesign (13.0.1). The tags won't show up in the file therefore not allowing the pdfs to pass the accessibility checker. The only work around I'm finding is to re-install the 2017 CC, save the files out as an idml and reopen and export from there. There are no issues when exporting as tagged pdf from the 2017 CC.