Much in the news of late; here, from Guardian:

Mystery of Japan sea's ghost ships points to North Korea
Bodies discovered aboard drifting vessels believed to be of soldiers turned
fishermen, as Japanese authorities concede puzzle may never be solved

In the past two months at least a dozen boats carrying the remains of 27 people have been found drifting off Japan’s coast.

Some believe those on the boats were defectors; others speculated they were spies. But the most plausible explanation is less dramatic.
much more at link above