Thought I'd share another mistake I made that caused thermal paste to be pushed through the COB onto its surface!
Hope it's not electrically conductive or spoils the COB in some other way...
Oops - thermal paste leaking through COB
I did some maintenance on my DIY fixture yesterday, and I see this some times. It's not a big deal, the TIM doesn't even cover the LEDs. (Even if it does, turn the lights off, let it cool, and carefully wipe with with a paper towel and alcohol. I did that already a few times, and my COBs work already for 4+ years like on the first day. They LIKELY used something like Arctic MX-4 (gray stuff), which is not conductive.