Running badblocks on 2 hard drives at the same time - percentage done difference increasing

[MazerRakham]

I am running badblocks on 2 18TB Seagate Ironwolf Pro drives on Windows through WSL2. For both drives, I started running badblocks on them at the same time, and there was virtually no difference between them in terms of percentage completed.

I am now halfway through the 2nd pass the the percentage difference is close to 20 (one is at 70% finished, the other is 50%). The percentage difference seems to be increasing over time.

So far, no errors have been found by badblocks, but is there reason to be concerned?