Did you customize some of the Seahub settings like mentioned in https://manual.seafile.com/deploy/deploy_seahub_at_non-root_domain.html ?
The *_URL variables need to match what you configured in Nginx, especially MEDIA_URL.
Maybe use the Developer Tools of your browser to find out which urls are tried.
Yes, I meant those (the request urls you posted before weren’t the ones that failed) - you see that it tries to access the subpath /seafmedia/ which you did not configure in the Nginx configuration you posted above (just location /media there).
Based on your Nginx configuration and your last post it isn’t quite plausible that this would have been the root cause, but if it works, it’s okay.
When using fastcgi, the location /media directory is not needed in the configuration and is why you are having issues. Remove that bit and clear browser cache should fix this issue.