Solution to light occasionally malfunctioning after battery changes
I finally figured out what was causing the problem where after battery changes, sometimes the light would only activate in low mode.
Apparently, I overtightened the switch retaining ring after modding. Doing so lifted up at least part of the board a tiny amount away from the tailcap. This sometimes caused a poor connection between the edge of the switch board and the tailcap. The light only turned on in low mode because of this poor connection.
The best solution is to not overtighten the retaining ring when modding. I did this by tightening it all the way, then loosening it by maybe 15 degrees.
Alternatively, removing the retaining ring also works. However, that causes the switch parts to risk being lost if you ever unscrew the tailcap.
Nubbin mod is not necessary
On another note, my second KR1AA arrived. This time, the only switch mod I did was to add a 9mm od by 1.5mm thick o-ring between the switch boot and the switch board. I didn’t touch the nubbin. The result is quite satisfactory. It is not necessary to remove the nubbin at all.
I don’t have any on-hand, but I expect using an even thicker o-ring would provide even more resistance.