Transient Power-off on both Zebralight SC64w & SC600w Mk IV HI

After setting +5°C PID, my SC64w and SC600w Mk IV HI both would turn off after working on H1 (i.e., the highest brightness level) for ~1hr, and this problem could be reproduced almost every time.

The battery used was NCR18650GA (65mm original, no button-top, nor protection circuit)

The max temperature I measured on the their surface is 48°C (SC600w Mk IV HI) and 54°C (SC64w). The PID did work and the temperature was not quite high (as a flashlight, if compared with products from some other brands). They simply should not behave that way.

Since my old SC600w Mk III HI works properly and never turns itself off like that with +5°C PID, I would say there must be something wrong with these two new flashlights I just bought.

And this problem didn’t happen on my SC600Fc Mk IV Plus and SC600w Mk IV Plus, even when their max temperature were also close to 54°C.

Runtime Curves:

Has this problem ever been reported or encountered by anyone before?

I have contacted Zebralight via the form on their website (cannot find their e-Mail). No response yet.