Hi,
I had a similar problem. In my case, I put 2x18650 (>7v) on a drop-in that was spec’ed for 1x18650 :).
Anyway, that was what got me started into modding, awhile ago, and I had a thread about my “adventures”:
In my case, it turned out that the emitter was killed, but there was no visible evidence, so I had to do the type of testing/diagnosis mentioned above, and in that thread.
Hope that helps…
Jim