SUN GTIL 1000W Power Drop Issue

It's been 3 years since I install this grid tied inverter setup, with 1000 watt GTI and 720 wp solar panel without battery.
But I experience very annoying behavior that inverter stop pulling electricity from the panel, drop to 0 watt randomly. Making the energy production is very low, I realize this because the production is drop significantly. Then I put my CCTV cam to see what happened.
Turns out, at the middle of the day, when the sun is shinning bright the power meter showing 0 watt.
For example, the GTI is pulling 500 watt of electricity, then without any sun changes, it drop to 0 watt for around 10 seconds and up again 500 watt, repeats and getting worse. It can be stay 0 for 3 minutes, goes up 500 watt for 15 sec and drop again to 0.
Sometimes it can stay 500 watt for longer time without drop, sometime can stay 0 watt for more than 5 mins.
Did you know what possibly wrong with this situation?
What I already do but didn't solve the issue:
1. Clean all connector
2. Clean the fan at the GTI inverter (fan working fine)
3. Try to unplug some of the panel. Use any panel = same behaviour. Posibly nothing wrong with the panel.
4. When it happen, I do plug unplug the inverter, nothing happen still drop to 0 randomly
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