40w laser tube lower voltage connector burn mark

Hi everyone:
recently I got a laser cutter from https://www.cncworld.nl/co2-laser-pl...int-p-122.html
I use always 30% power and cutting speed is 10mm/s. I always check for air bubbles before use. after a few times of use, I notice the lower voltage connector from the tube has a burn mark.
and after a while, it got worse. and I stopped using the machine. I contacted the seller Matheus from CNCworld. He doesn't respond to email for days. and doesn't give me any suggestion or advice only saying that I can't return the laser cutter.

I hope someone can help me with debugging the issue here. what should I do? Maybe I should redo the insulation? I just ordered some electrical grad silicon.
Any suggestions and help will be appreciated !:-))))