My EDC started to fail recently.
Sometimes it would work OK but sometimes it wouldn’t turn on.
When I saw this the first time I thought it was LVP. It was not.
I tried cleaning electrical contacts - that didn’t help.
If it works it works - there are no issues with mode changes which rules out the switch.
I had the same problem. The fault was indeed in the wire that is connected to ground. It is necessary to remove the lens and check the ground wire to the lamp housing.
The ground wire is soldered to a thin screw. it is screwed into the flashlight housing under the lens. At my flashlight, the screw had bad contact with the flashlight housing.
Mine also had a good solder connection, but the screw was loose. I cleaned all the solder off the screw head then tightened it up with a mini screwdriver. Resoldered the white wire and it’s now perfect.