First you can try without reinstallation:
signal-event nethserver-backup-config-update
signal-event nethserver-backup-data-update
If still not working, you can force reinstall backup module (but from the rpm commands above seems all module files are present):
yum reinstall nethserver-backup-config nethserver-backup-data
If it does not work, for other required packages there was this command:
yum update @nethserver-iso
But it is strange that the browser console doesn’t spit some warning or error message… (on the other hand maybe browser’s network stats could tell if it is stuck for long time trying to acces some file…)