Hi @Vianneybdx - I've had an issue like this in the past, it was due to the carrier (not the app).  I think it depends on who your mobile provider is, how strong your signal is (how many bars of 4G), and if you may have hit some sort of cap/threshold for data transfer and are being throttled.  (also, depending on the photo/video quality, could be quite a large file)

This may not sound terribly helpful, but my resolution was to upload the photos after the fact (when I was on wifi).  This saved headaches (as well as potential data charges from mobile carrier).