I asked the etcher team and they think this is probably related to this issue: Lock the drive to prevent failure on verification · Issue #3197 · balena-io/etcher · GitHub
In a nutshell, it means that the data Etcher reads from the device is not exactly the same as the one in the disk image that was written.
Most likely your image was flashed correctly but something wrote some files to the drive before the validation completed, changing its checksum. This can happen specially if you are running etcher on Windows. To avoid it, you should follow the instructions here How to prevent creation of "System Volume Information" folder in Windows 10 for USB flash drives? - Super User. That said, the validation step is not actually required, it’s just an added feature to verify the image was flashed correctly. You can try booting the SD card and see if that works.
The alternative scenario is that your SD card is broken and doesn’t write or read all the data it gets asked to. Since you say it’s a brand new card this is most likely not the problem, but worth checking if you have a spare one.