Happened today, yesterday.
It just keeps happening.
You sure it’s not just a Linker? I’ve been fooled once or twice by a Linker hitting a target and walking away.
I can be a judge for that. The shining mob appeared in front of me. DIdn’t drop anything, A Kepari Mob
When you face a shining mob, check under its name (around the middle of the screen), see if it has a buff that look like a green 4 leaf clover. Screenshots would help a lot. (When I played before 2nd Apr, shining mobs still give bonus)