User syncing throws error at the beginning and stops after 40 to 50 users synced

When triggering user sync from master site http://eunamed.com, it stops after syncing around 40 to 50 users.

Also, when just starting syncing, we get an error as you can see in the screenshot attached in the next message.

Im also attaching in the next message the error logs indicating which one's mastersite and substie.