If you have multiple file upload controls on a nintex forms for office 365 form you can pick which upload control the added attachmenta go to but you can only pick one so unfortunately, to my knowledge anyways, there is no way of pointing specific attachments to a specific file upload control on a that particular nintex form if having multiple. 

@brandiwoodson Bummer.. even in a NAC form?

I think you will most likely need an additional document library for the attachments. Maybe create a folder for each workflow instance and store all the attachments in the folder.
On the main list have a URL field for each section which holds the link to the attachment rather than an attachment on the list item itself.

You may have to think outside the box on this one and somehow add your attachments in a library instead with maybe a lookup field back to the list item and a category field that represnts which files belong to which section....wuery all your fikes back that relates to the list item and buikt a text string per category and display in a label. You need to store the html text string in seperate text fields in your list.

Sounds like a bit of a complex fix  

Thank you for your suggestions @Deon & @brandiwoodson! Appreciate it