Ran into the same thing yesterday, I think in our case caused by our patching system rebooting the tape server in the middle of a job. Trying to restore files from the problem tape yielded the same thing. Luckily the source vbk wasn't yet deleted from retention cycle so we just did a quick erase on the tape and it started working fine. Our tape is a virgin Veeam tape so no difference in format, etc. It just appeared to get goofed up by the server rebooting during use.
Veeam B&R v9
Dell TL2000 via PE430 (SAS)