After a year of fairly light use, the lens holder (and “attack ring”) of my J5-V2 flashlight worked loose and began to rattle. The ring holding the lens in place turned out to be finger-loose, but that wasn’t the entire problem, so I removed it and looked inside:
The mysterious alien egg resides on the upper-right side of the LED emitter.
The aluminum ring holding the LED assembly in place was also finger-loose, so I unwound it to take the whole front end apart:
Reassembly with a few dabs of Loctite in appropriate places should prevent future rattles.