BitmapHeader Signatures not equal error restoring backup A quick update on the issue.
Here's what was found:
1) The disk where the backups have been stored died(hardware failure) and data was restored using third-party data restoration tool.
2) During disk restoration using that third-party tool it corrupted encryption headers of our backup files, making them unrecoverable. There's also a chance that they were simply corrupted during the disk failure, we'll never know at this point.
For some reason that crucial part of the problem was not mentioned neither by you or your colleagues initially, but we finally got to the root of the issue.
Even though our software is not at fault here, we'll do everything in our powers to restore your data.
To avoid problems like that we recommend using cloud backups along with the local ones, so that if you are faced with a hardware failure the files can always be recovered from the cloud.