Yes they can get too large for reliable online backup.
We had regular problems with backups that were 2-3 Gigabytes. When we had Guardian Angel Support help us they had us turn off imports & pics. Online backups are now 99% plus reliable. Our ImportedItems folder is now 16.5 GB and our .enc backup file is about 1/3 of a GB. The longer timeframe the inline backup takes the more likely it will have some internet problem. Also, we found our cable ISP was cutting off any process running at midnight so we schedule them to be done before then or start after.
