Access token generated with refresh token got permissions revoked

As per the dropbox offline flow, I've set up a flow where I've generated a refresh token after the owner of the dropbox (me) 
- Generated an access code using this URL
https://www.dropbox.com/oauth2/authorize?client_id<YOUR_APP_KEY>&response_type=code&token_access_type=offline
- Used the access code to generate a token using this request
curl https://api.dropbox.com/oauth2/token -d code=<ACCESS_CODE> -d grant_type=authorization_code -u <APP_KEY>:<APP_SECRET> 

I was succesfully generating an access token with the refresh token that I got and my files were being uploaded.
After a month I come back and I get errors that my token no longer has permissions to do so.
This should not be the case since I did not set an expiration date on the refresh token or revoked any permissions.

Because this flow starts with an owner interaction, it cannot be restarted with an app in production as many uploads will be lost.
A new refresh token was generated and it all works now, but again I don't want this to happen in production.

How do I solve the issue?