Sorry to hear that there are some failures generating backups and our team is happy to help in any way we can.
There isn’t a defined limit on the size of backups that you can generate using Total Upkeep, but you can sometimes see backups failing in shared hosting environments when the backup size is greater than 2 GB. These failures are usually related to the amount of available resources that are allocated for your installation and generally shared platforms have strict limits that might be automatically terminating the backup process as resource usage grows.
Creating backups through PHP processes, which most website based backups solutions use, can be resource intensive when handling larger websites. In the Settings for Total Upkeep there is a Backup Process option and switching the processor to System zip uses the server’s Zip functionality instead of a PHP process to generate backups, which might help mitigate those failures.
Please let us know if you have any additional questions!