Problems running Managed Backups, restoring Snapshots and max_execution_time

Snapshot Managed Backups aren't being performed since a week ago. I've tried changing the keys, deleting the files I had, but it's not working…
And I have this error: “Other kind of backup error”.
Local and Dropbox Snapshots are going fine. But I can't restore a Snapshot from my Dropbox (I've followed the instructions, placed it on my Public Folder in my Dropbox and placed the link to the file), it returns some "Manifest" not present but was created last night by Snapshot itself...
"Twice a Day" option should return for backups (both Local and Dropbox, not Managed)...

Also, I have max_execution_time set to 300 and in the WPMU DEV Dashboard System says is 0.