OP, you suspect the real problem in your post earlier today.
Look at the mobo manual on p. 48 where the fan header pinouts are shown. For the CPU_FAN header, Pin #2 says "+12V", and Pin #4 says "Speed Control Signal". THIS header is using PWM Mode for control. Now see the labels on ALL of the other headers, Pin #2 says "Voltage Control", and Pin #4 says "NC". All of these headers are using the older 3-pin method called Voltage Co0ntrol Mode, and do NOT put out a PWM signal on Pin #4.
This latter type of header has become very common lately. It is the simplistic way to make a "universal" fan header. It CAN control 3-pin fans because this is the only method that works for them. It also CAN control 4-pin fans because they have a backwards compatibility feature in their design. When a 4-pin fan receives no PWM signal from Pin #4 it cannot modify the voltage supplied on Pin #2 to alter the motor speed. BUT the voltage on Pin #2 is NOT a fixed +12 VDC, as a true PWM Mode system would provide. It is a VARYING DC supply, ranging from 12 to 5 VDC, just as any 3-pin fan header would do. The 4-pin fan motor gets that voltage, whatever it is, un-altered by a non-existent PWM signal, and the motor's speed IS controlled that way.
This design works for both 3-pin and 4-pin fans when only one is plugged into the header. It also works for either fan type if you use a SPLITTER to connect two or more fans to that header. A Splitter merely connects the fans in parallel to the header's voltage supplies. But when using a Splitter, you must consider that the header has a limit of 1.0 amps total current max to all fans connected to it. A HUB is a different device. It gets power for all of its fans from the PSU directly using a SATA or Molex output. It gets the PWM signal from the mobo header it is plugged into, and merely shares that out to all its fans. Then it is up to the fans to use the PWM signal internally to modify the voltage supplied (from the PSU, fixed at 12 VDC) to achieve speed control. Thus a HUB MUST have a PWM signal to share to its fans, and it can ONLY achieve control over 4-pin fans that can use that signal.
You say you have "Noctua Redux S12B" fans which are 3-pin models, but I bet yours are really the "NF-S12B Redux PWM" model with 4 pins. The problem you have is that the Hub (and hence the fans) is NOT receiving any PWM signal from the mobo header, so all those fans are not able to use it to modify the fixed +12 VDC supply coming from the PSU.
The solution is to NOT use a Hub, but change to using Splitters. In many cases this is not quite suitable, but for you it happens to work. Those fans (1200 rpm model) are spec'd at 0.075A each max current, so even 8 of them in parallel will consume 0.6 amps max, which is within the capability of one fan header. If you want to be cautious, get two Splitters and use them to connect only 4 of these fans to each of your SYS_FAN1 and SYS_FAN2 headers. To help, a SPLITTER has an input arm that connects to the mobo header and outputs for fans, but it has NO arm to connect to a PSU output. For your purpose, I suggest a Splitter that looks like a small printed circuit board with several male (with pins) 4-pin fan headers on it and one input cable. Here's an example
https://www.newegg.com/Product/Product.aspx?Item=N82E16882422016&cm_re=Coboc_fan_splitter-_-82-422-016-_-Product
Although the four ports on it are Labelled "CPU" and "Fan1 to 3", plug a fan into the "CPU" header on each one; do not plug your CPU cooler into these. Plug each Splitter into one of your SYS_FAN headers. The all these Ncotua fans will be fed the Voltage Control Mode signals from those mobo headers and their speeds WILL be controlled by those signals.
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