Hi,
For the ColdClam site, it looks like you need to re-authenticate with Dropbox. Can you please try to Wipe settings from UpdraftPlus > Advanced tools > Wipe settings, Click the ‘wipe settings’ button. Then re-setup your Dropbox
Arnica- Can you install the free plugin WPCrontrol and navigate to the Cron events. Do you see any overdue tasks?
Regarding your question about storing your backups, if you go to the Settings tab you should be able to set your retentions limits. In the bit that says “..and retain this many backups” what do you have here?