No, they are not there.
just to give a little more info, I tried yesterday night again. the app its trying to backup around 950 pictures at somewhat 4MB each. when i check the logs i see requests like the ones below as the number of “remainig pictures” decrease. at some point i managed to see the number of remaining pictures at 600. but no trace of the pictures when checking through the browser on my laptop.
126.96.36.199 - - [13/Jan/2020:20:30:58 +0000] “POST /files/2737a4e1f9842b39c0b0492f3c02c96d?Name=IMG_20181212_195202.jpg&Type=file&Tags=library&Executable=false HTTP/2.0” 499 0 “-” “Dalvik/2.1.0 (Linux; U; Android 8.0.0; ONEPLUS A3000 Build/OPR1.170623.032)”
188.8.131.52 - - [13/Jan/2020:20:30:58 +0000] “GET /files/metadata?Path=%2Fmobile.settings.media_backup.media_folder%2Fmobile.settings.media_backup.backup_folder%2FIMG_20181212_195203.jpg HTTP/2.0” 404 93 “-” “Mozilla/5.0 (Linux; Android 8.0.0; ONEPLUS A3000 Build/OPR1.170623.032; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/79.0.3945.93 Mobile Safari/537.36 io.cozy.drive.mobile-1.18.24”