From GameWatcher: “Jabber Mogwai is one of the more unique Legendary Hunt bosses in Borderlands 3, mostly due to its tendency to duplicate itself under certain conditions. We’d have written this off as a bug, but it might not be the case.
If Mogwai’s name sounds familiar, that’s because it’s a clear reference to 90s classic Gremlins, which also makes us think its duplication might not be a bug, and therefore may not get fixed in a future update, unlike certain other XP farming techniques.”
Source: N4G PC Borderlands 3 Jabber Mogwai – How to Duplicate the Boss?