Because you're doing it with the power on.
That is to say, during daytime. The arc should go away if you turn off the solar panel. Either throw a tarp over it or wait til night.
Also, try to get out of the inverter business.
Try to arrange things so your loads run directly off 12V instead of off the inverter. The worst sin I see is people running cell phone chargers off inverters. Every gas station, big-box and 7-11 sells cell phone chargers that run on 12 volts.
Certain loads like a refrigerator need to be on inverter. But try to find a way to spin up the inverter only when needed. An ideal setup would be to spin up the inverter hourly, and then have it shut itself down when current draw stops (after the fridge has cycled and quit).
As far as quality ratings, that's on you. You can choose to buy quality stuff or save money, and you endure the result of that. I can tell you "cheap Chinese" isn't anymore; they now charge retail prices as high as 95% of the genuine/quality units. Paying a lot is no longer an assurance of quality.
As far as sizing the system (how big solar vs how big battery vs loads), that is the usual place people go wrong, because they have not bothered to learn the concepts.
It takes some time. Hang out on off-grid solar power forums and such. (SE isn't the right forum; we don't field nearly enough questions about off-grid). You'll get exposed to a lot, such as "don't use more than 1/3 of a lead-acid battery's capacity", what a watt-hour is, how much common loads take (modern refrigerator: 1000 watt-hours per day), how to size solar panels to allow for winter and cloudy days, battery versus your expected draw, etc.