Newty said:

Do you have a multimeter?
Start checking power and continuity at the different connections.

The 4 connections on the outside don't look like they have any wires going to them, I'm assuming they are for bridging/chaining more boards together. Can you remove the wires at the middle of the boards and move the wires so power is going through the unused connectors? This should eliminate the current connections being used on the board as being the issue.
If moving the wires changes which leds are not working, then the issue would be between those 2 points.

If you're looking for new boards or drivers, check out HLG's selection! They have a good selection for diy!

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LoveGrowingIt said:

It could be a weak or corroded connection. Does it have a variable power knob? If so, move it rapidly from high to low a few times. That can scrape off corrosion. The same is true for wired connections (the plugs) so sliding them in and out can do the same thing. It could also be the line power, so adding a line conditioner might help. That would be a good-quality surge protector or a UPS. Other than that, it could be a weak capacitor or some other problem in the rectifier circuit. Fixing that wouldn't be easy. It would be easier to buy a new driver. If it's that, then buying a new light probably would be the best option.

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Galgrows said:

Somewhere theres a short in the wires. LED so cheap nowdays and good ones just treat yourself to a new one

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