iCloud Photo upload stuck

Hello

I've been trying to upload my photo library in iCloud since 3 weeks, and I don't see a significant progress so far.

The upload gets stuck at the beginning (c. 25 000 photos, 3 000 done, remains 22 000 and stuck).

I tried to reconnect iCloud in the settings as I found the advice on internet, it restarted from the beginning and got stuck again.

If I go into the Console, I have a strange message "com.apple.photos.VideoConversionService" and "Ignoring request to send progress update for job (#series of letters) in non-queued/running state 4"

For the moment, I stopped it for the day (I already tried that once without success).

Photos are also uploading at the same moment from my phone (very slowly as well).

Any idea what could be the issue ?

I'm using macOS Sierra on an iMac mid-2011.

Thanks,

Mickael.