exporting from premiere to dropbox results in 1ko video

hi, i've been using dropbox to store all my edits online for a year now and i've always export my videos directly to some dropbox folder because all my files are organized in dropbox. 

Since a month or so everytime i do an export to a dropbox folder it results in a 1ko video witch is unreadable 

do you have any idea why is this happening ? or how can i fix it