I tried version PowerCLI 11.0,,and get the below..
Next may be to try to restore to the same ESXi 7.7 version?
PS C:\Windows\system32> Set-VMHostFirmware -VMHost 128.244.170.100 -Restore -Force -SourcePath c:\ESXi-Backup\configBundle-192.168.10.12.tgz
Set-VMHostFirmware : 6/11/2019 2:46:16 PM Set-VMHostFirmware A general system error occurred: Internal error
At line:1 char:1
+ Set-VMHostFirmware -VMHost 192.168.10.20 -Restore -Force -SourcePat ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Set-VMHostFirmware], SystemError
+ FullyQualifiedErrorId : Client20_SystemManagementServiceImpl_RestoreVmHostFirmware_ViError,VMware.VimAutomation.ViCore.Cmdlets.Commands.Host.SetVMHostFirmware