Few attachements failing to upload

Hello Folks,

Few attachments like pdf & others are failing to upload for a specific user.

Txt were getting uploaded.

Error:

We couldn't save your attachment Reload the issue then try adding it again.

Kindly help to figure the root cause.

See this in web developer console:

XHR PUThttps://api.media.atlassian.com/chunk/sha256-becbe905d7d1a08bdb4aa2d62729d72e03221cd9dbc4da2aa9e4996b9338dc74-498931?partNumber=1&uploadId=c6ff1dbd-7225-4b77-936f-97ca4e68cacf[HTTP/1.1 403 Forbidden 344ms]