Content type showing as */* on submission attachments

1. What is the issue? Please be detailed.
many submission attachments have '/' as content type in blob table. For some submissions the content type is getting set properly as application/pdf. I would like to understand for which scenario does content type gets set to '/'


2. What steps can we take to reproduce this issue?
upload pdf files to the deployed form. And check the content type of uploaded file using query:

select, sa."name" , b."contentType" from submission_attachments sa
join blobs b on ( = sa."blobId")
where sa."name" like '%.pdf' and b."contentType" = '/'

What version of Central are you running? Did these submissions come from Collect or Enketo? If Collect, what version? What's the rough range of the submission dates? Any chance these submissions were edited in Central? What's the rough range of the edit dates?

My guess is that there was a bug in an old version of Central or Collect or Enketo that was fixed. Answering the above questions will help us narrow down the likely culprit.