See Bo 10:22, and Rashi's words about the phrase, "Vayhee Hoshech..."
Rashi notes that "Posh'ei Yisra'el" were purged during Hoshech. I've always been troubled by this statement. If all the reshaim died during Makkat Hoshech, then how did ones like Datan and Aviram survive?
A clue lies in Rashi's own words. Rashi wrote that ONLY those "shelo hayyu rotzim latzeit" were killed.
IOW, only the ones who wanted to stay in Egypt were killed. It seems that while only one SUBSET of Posh'im were purged, other "nudniks" seemed to survive. These may be the ones we see causing trouble in the Midbar later.