BLF Kronos X5 mod x6 mod faq thread tailcaplight

I received my X5 a few weeks ago directly by manker (Donation to Old-Lumnens (finished) )

I really like it in general and the lighted tailcap is pretty useful. After I used the light for about 30 minutes continuously the tailcap started to behave strange. The tailcap light is now dimmer than it was before (yes, even after recharging the battery) and it flickers sometimes. I was not able to take apart the tailcap yet, since the retaining ring sits tightly.

Do you guys have any ideas what is causing this?