Eh, Hoppers I don't worry about. Jumpers, OTOH, Are a negative.

The difference (at least to me) is time. Hoppers are people who typically change jobs every 1.5-3 years.

Jumpers, will have a long history of 6 month stints, very few if any gigs longer than a year. At most places I've worked, depending on the quality of on-boarding it took most engineers 1-3 months to be productive, and 3-12 months to understand the system well enough to make impactful changes to the ecosystem safely.