Before asking others for support, please remember that they need a reasonable amount of information in order to help. Depending on the issue, here's some important details to include:
What kind of LED's you're using.
What microcontroller board you're using.
What version of the FastLED library you're using.
What version of Arduino IDE you're using.
What
OS you're building from.
A circuit diagram/layout (try using Fritzing to show it).
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Essentially, give us EVERYTHING in excruciating detail.
Provide specifics on how/where it's all being powered up.
That would be pins, voltages, power supply used. . . every . . single . . wire.
Try and remove all the superfluous code and minimize the amount of code that exhibits the issue.
Oh, and triple check EVERYTHING. Again!