Hi Paula,
To help us work out the cause of your problem, can you please send us a copy of the backup log?
This log can be found in the Existing Backups tab of the UpdraftPlus dashboard.
The contents will be too long to post here directly, but you can use an online service such as Dropbox or Pastebin, and post the link here.
It is not currently possible to manually change the resumption interval. This is adjusted automatically by UpdraftPlus.
Intermittent internet connectivity on your local machine will not affect a backup on a hosted site.
Best Wishes,
David