You are exceeding the ability of your only SYS_FAN1 header. Like most, it can supply up to 1.0 A total current to all fans connected to it. You have six fans by Corsair. Unfortunately their website does not tell us the max current for one fan's MOTOR only - the specs appear to be total for fan motor and lights combined. But the few Corsair fans like that with NO lights draw 0.225 A max each. Six comes to 1.35 A - even five is over the limit!
As Lutfij said above, you need a fan HUB. The Splitters you have used get all fan power solely from the mobo header, and it cannot supply that much. A HUB is a different device that can work only with a header using the new PWM Mode of control, and only with 4-pin PWM type fans. That IS what you have. The Hub is different because it has an extra connecting "arm" (or a edge connector) that must connect to a SATA power output from the PSU directly. It gets all power for its fans from that PSU (much higher limit you won't exceed) and draws none from the header. It does get the PWM control signal from the header and share it to all the fans, but that is not a current-limit issue. And it does return to the header the speed signal of only ONE of its fans - the one plugged into the marked output port. A Hub may look like a collection of arms the way common Splitters do like this
Note on that page you need the one that gets power from a SATA power connector. And note that is has only ONE output with all 4 pins - that is the only one that sends its fan speed signal back to the host header.
A Hub may look like a circuit board like this
That has an edge connector for SATA power. Its RED output marked "CPU" does NOT need to be used for the CPU cooler. It is the one output that sends its fan's speed signal back. When using this type you must mount it securely so it does not shake loose and short out to the case.
A Hub may look like a box with ports in the sides like this
It has one port marked with a speedometer icon and comes with cables to connect to your SYS_FAN1 header and a PSU SATA power output.
I chose all of those examples with 6 outputs or more. Some come with fewer. BUT you COULD use a Hub with 5 or less outputs, and use one of your existing Splitters from one output port to connect more than one fan there. Since all power to the Hub output ports comes from the PSU, this would not exceed the power limit of the header.