If the low voltage coloured rainbow is showing up then the voltage is dropping too low, there’s nothing the software can do that would cause the symbol to appear when the voltage is not low, so you definitely have a low voltage issue for whatever reason.
(The symbol appears when a hardware voltage comparator sends a signal on a GPIO pin to the GPU firmware which displays the symbol - all completely outside of the control of the Linux OS)
The total power drain can vary based on software demands, overclock and so on, so a change to the power demands of the software could push a marginal setup over the edge, but at the end of the day it is still a hardware issue.
What USB devices do you have connected and what overclock setting are you using ?
I don’t suppose you are using the sdhost test kernel posted in another thread ? A change was made to that kernel which results in the CPU being put into turbo mode whenever there is disk activity (eg much more often) which would increase power demands, but unless you have manually installed that kernel it won’t be affecting you.
As mentioned in this thread, the transmission app in the App store is not currently working: