All restored files are corrupted

Hello, we hase some days ago a ransomware attack but we was happy to have a backup.
We restore all files now but we have the problem now that all Files are corrupted and we cant open it.

For Example a pdf.
The Computer and also the Server are installed new anitivirus up to date and all systems scanned.

LINK with screenshot :File corrupted

This problem we have with all files like word, excel, Powerpount, pdf ect. ect.

Do you have an older backup you can check? It’s possible they were backed up after the ransomware got at them. Have you checked on the backup storage to determine if they’re corrupt there to eliminate the possibility that something went wrong with the restore process?

i have chek older Backups, same issue.

BUT
I found out, when i download the file as ZIP and extract it at the restored folder, i can open the file.
My Problem is now that i have thousends of files and older, so download all in zip and extract is not aq good solution.

For info, using UrBAckup Server 2.4.13 - Client 2.4.10 on Windows Server 2016 ( Backup Server and Restored Server )

No one have this problem ??
Need realy help about the issue, cant restore over 5 TB of backups on that way.

I have experienced this issue.
The very large ZIP files are often corrupted.
I installed the backup client on a clean, no virus, system then did restore.
All the data restored to the original folders correctly.