I don’t know how this was working before. Assuming that the ‘pdf_brochure’ ACF field is a file field, ACF has always stored the file ID in the database. It only returns the url if set to do so when using get_field() or some other ACF function. If the CF7 addon is getting the value of the ACF field then it could only get the ID unless there was some other filter being run for shortcode [dynamichidden dynamichidden-468 "CF7_get_custom_field key='pdf_brochure'"].
Unfortunately, I cannot help you with the CF7 add on and what may have been going on before. You’re best bet to get help with this would probably be support for the other plugin.
