Hhmm, could be the heat, improving contact. Could be a few things, power, ground, driver, LED connection, etc.
Review here, not so complementary: https://budgetlightforum.com/t/-/48611#comment-1231789
It looks like 4 cells in parallel, and the LED's are 12V, so needs a boost driver. I think the batteries would draw 6-8 amps on max/turbo, assuming 2 amps and 12V per LED. So your batteries need to be fairly good. Probably not the batteries but worth checking. I would clean the brass ring where batt+ makes contact - use a little sand paper and/or isop. alcohol. Also where the batt tube connects up to the housing head. Check the springs - also clean contact surfaces there with isop. alcohol. Oxidation can build up over time and it's not really visible. That's like the easy stuff that you can get to.