Let me clarify the two different types of devices that allow you to connect more than one fan to a single mobo fan header. The problem here is that makers and sellers use the two names as if they were the same, and they are NOT.
A SPLITTER is a simple device. It has one "arm" with a female (with holes) connector to plug into the mobo header. Then it has two or more output "arms" with male (with pins) connectors where you plug in your fans. It may actually look like a collection of cable arms, OR a small circuit board, OR a closed box with holes in the side for the recessed male outputs. But it has only those two types of connections. All it does it connect all the outputs in parallel to the mobo header signals. All power for the fans comes from the header, which normally is able to supply power at 12 VDC up to a limit to if 1.0 A max total current. When you are using 3-pin fans, you MUST use a SPLITTER.
A HUB is a different device, and its appearance may be almost identical to those three forms above. What is DIFFERENT about is it that it has a third type of connection. It requires input of power directly from the PSU via either a 4-pin Molex or a SATA power connector. This device gets all power for its fans from the PSU and draws none from the host header, so it avoids that current limit. HOWEVER, because of its design a HUB can work ONLY with a header that does use the newer PWM Mode of control signals, and ONLY with the new 4-pin fans. If you plug an older 3-pin fan into a Hub output, there is no control of speed of that fan and it always runs full speed.
IF you have a mixture of many fans, arrange them so that one group of 4-pin fans uses a HUB and a header set to use PWM Mode, and the other group of 3-pin fans uses a SPLITTER and a header set to the older Voltage Control Mode (aka DC Mode).
The design of the newer 4-pin fans made sure the two types were as closely compatible as possible, so mechanically and electrically you CAN plug any 3-pin or 4-pin fan into any 3-pin or 4-pin header. If you mis-match them, this is what happens. A 3-pin fan fed by a 4-pin header in PWM Mode cannot have its speed controlled so it always runs full speed. You get lots (more than necessary) of cooling but no ability to reduce speed. A 4-pin fan plugged into a header using the older 3-pin Voltage Control Mode WILL operate AND have its speed controlled, even though this is not the "ideal" control signal system for that fan.
Because of all this, almost all current mobo headers have 4 pins. BUT for each header in BIOS Setup you can set a configuration option for whether that header will act like an older 3-pin header in Voltage Control Mode (aka DC Mode), or as a newer 4-pin header in PWM Mode. Many such headers also offer an "Auto Mode" that tests the connected fan at each start-up and sets the Mode according to the result. This works just fine for most situations, but it causes a problem sometimes with AIO liquid-cooled systems for CPU's.
Any mobo header has an important secondary function. It receives from its fan a speed signal consisting of pulses to count. It can show you this speed for your info but it does NOT use that for its speed control function. It DOES monitor that for NO signal, indicating fan FAILURE. However, it can deal with the speed signal from only ONE fan. So when you use either a Splitter or a Hub that device will send back to the host header the speed from only the ONE fan plugged into the marked special output, and ignore all the other fans' speeds. In a "collection of arms" style device, only one of the outputs has all four pins; in all the others Pin #3 is missing. That is the pin for the speed signal line, so omitting that means the speed signal can't be connected back to the header. For other physical forms there is a mark of some kind to indicate the only output that sends the speed back. In all cases you should ensure that there is a fan plugged into that identified output. Note that for purposes of fan FAILURE monitoring, only that one fan's speed can be checked and the header cannot "see" failure in other fans on that Splitter or Hub. So from time to time YOU should check fans to be sure they all still are working.
From all this you can see that you do NOT need a Splitter or Hub with both 3- and 4-pin connectors. But you DO need to choose the correct type of multi-fan device, and the correct header configuration setting. How to choose?
1. Any header is limited to no more that 1.0 A max current in total to all fans on that one header. Each fan should have a spec for max current draw. It may be in published specs, or may be on the fan's label. IF the info given is in WATTS and not AMPS, use this: Watts = Amps x Volts, and max Volts always is 12. So max AMPS = max WATTS/12. Typical fans today have max Amps of 0.10 to 0.25, but look for the actual values for your fans. Add up the Amps max for all the fans you plan to connect to one header, and that cannot exceed 1.0 A IF you plan to use a SPLITTER. However, if you plan to use a HUB that gets power from the PSU, that header limit does NOT apply.
2. To be able to control the speed of older 3-pin fans you can ONLY use a SPLITTER, and the host header MUST be set to Voltage Control Mode (aka DC Mode). You ARE limited to max 1.0 A current for this fan header.
3. When using 4-pin fans ONLY, you can use either a SPLITTER or a HUB, but the host header MUST be set to PWM Mode. If you choose a HUB, the max current limit of the header does not apply, but it does apply if you choose a Splitter.
4. So if you have both fan types, it is best to create two groups. ONE group is all 3-pin fans using a SPLITTER to connect to a header set to Voltage Control Mode. The current limit of the header applies to this group. The other group is all 4-pin fans using a HUB and a header set to PWM Mode. The header current limit does not apply to this group.
5. IF you must (or sometimes it's just a choice) you CAN mix both fan types on one header by making use of the fact that the speed of newer 4-pin fans CAN be controlled by the older Voltage Control Mode. For this scheme it is just like using only 3-pin fans (above) with a Splitter and Voltage Control Mode, and the amp limit does apply to this header.
So, OP, look closely at the "Fan Hub" you already have. In my way of using the labels, is it really a HUB with a connection for power to the PSU AND a connecting cable that goes to a mobo header? OR is it really a SPLITTER with ONLY the cable to a header and NO connection to the PSU? OR (third option) does it have ONLY a connection to the PSU for power and NO cable to a mobo fan header? For any of these three possibilities, make sure the connections are secure at all points, PLUS check each fan's plug into the "Hub".
Now look closely at the connectors on the end of each FAN's cable where it plugs into the "Hub". Do they have 3 holes or 4? THAT tells you which type of fan they are, and thus which way they can be connected for power and speed control.
Post back here with results and we can narrow down how to connect.
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