24°C temperature
i believe it's the fans, not the Octo that cause the confusion
the fan curve sets a PWM% of 0, and the X3M will default to full speed at that setting.
To use the 0 RPM feature of X3M you have to get idle temperature somewhere between 1 and 25% PWM
under 25% : they stop
at 0%, they default to full speed.
If you don't mean to have the fans stop at all, set your lowest speed in the fan curve to 26% or higher
An example would be a curve going from 22°C water temp at 26% fan speed , to 50°c at 100%