Hi, I have tried updating permalinks, reinstalled, deactivated and everything else. Kinda hard to see anything with multisite on demo since the demo is not multisite. As we are all saying, It is working on the main site, its just not working on a subsite. this is on fresh install, a number of fresh installs. Nothing activated except BP and RTmedia. On my subsite, the uploaded images from activity stream are not being uploaded, they are not being added to wall posts folder or are they in media gallery in the back end. They simply are not being uploaded on the subsite. Main site everything works like a charm.
like I said, for me, everything worked great up until the 3.10.9 update. I can give you credentials and ftp to log into my site if you would like to check things out.
here my debug info
Home URL https://zinckles.com/central Site URL https://zinckles.com/central PHP 5.6.22 MYSQL 5.1.73 WordPress 4.5.3 BuddyPress 188.8.131.52 rtMedia 4.0.2 OS Linux Imagick ImageMagick 6.7.2-7 2016-05-09 Q16 '<a href="http://www.imagemagick.org" target="_blank">www.imagemagick.org</a>' GD bundled (2.1.0 compatible) [php.ini] post_max_size 8M [php.ini] upload_max_filesize 32M [php.ini] memory_limit 256M Installed Plugins rtMedia for WordPress, BuddyPress and bbPress by <a href="http://rtcamp.com/?utm_source=dashboard&utm_medium=plugin&utm_campaign=buddypress-media">rtCamp</a> version 4.0.2, <br/>BuddyPress by <a href="https://buddypress.org/">The BuddyPress Community</a> version 184.108.40.206 Theme Name Twenty Sixteen Theme Version 1.2 Author URL https://wordpress.org/ Template Overrides plugins/buddypress-media/templates/media//album-gallery-item.php, <br/>plugins/buddypress-media/templates/media//album-gallery.php, <br/>plugins/buddypress-media/templates/media//album-single-edit.php, <br/>plugins/buddypress-media/templates/media//media-gallery-item.php, <br/>plugins/buddypress-media/templates/media//media-gallery.php, <br/>plugins/buddypress-media/templates/media//media-single-edit.php, <br/>plugins/buddypress-media/templates/media//media-single.php, <br/>plugins/buddypress-media/templates/media//uploader.php Total Albums 1