Got a KDLITKER P6-NIC drop-in for an old Surefire 6Z; Nichia 519A 800 Lumens 3V-9V LED module from Kaidomain. Three modes, Lo, Med, Hi. Put in two brand new Surefire 123A batteries. Does not work well: it flashes on Hi mode, briefly Hi and immediately changing to Low and flashing. That should be the low voltage indicator. Why? After a few tries it started to do the same at Med.
Put in regular Duracell Ultra 123s and it flashes on Low and Medium, but Hi seems to work well.
So you’d have the version that can be set to 3 or 5. Most likely not the issue, but something to be aware of given it mentions flashing when setting the groups.