There is currently a problem with the Object Storage from OVH that is used to serve media files for Masto.host and this is affecting both loading uploading of media.
They are already working on it: http://travaux.ovh.net/?do=details&id=47465&
Sorry about this. Hopefully they fix the issue soon. I will post here when I know more.
@Nikolai_Kingsley Glad you didn't notice :)
This one was really strange because it failed randomly but it was some issue on OVH internal network, nothing I could really control.
Church of the SubGenius Members-Only MastoDobbs.