Before starting to mess with the flashlight I would try and contact Hank at IOS insted. He’s got a good reputation of sorting out these sort of problems.
And I would bet it is a battery fit (probably length) issue, which seems to be a common problem with small form 18650 lights. Try a few different cells in it.
looks easy to add 3 more 7135’s hehe…. to make a thermally unstable beast!!! 