I have the same issue mate, everything you described above. I also checked the PCI card, underneath the heatsink and the brown cable was perfectly connected to the Intel chip. I also checked the brown cable inside the transmitter, also there it was connected. The coax cable on the PCI end is tightly placed.
The Intel drivers are all installed. I even installed Intel's DSA program to check for every Intel hardware that's not up-to-date but couldn't find anything.
As for my PC, it's BIOS has been updated to the latest version. The motherboard is a B450 Steel Legend on a Ryzen 5 3600 CPU. OS is Windows 10, which is also the latest release. Not sure if the RAM is relevant in this case though..
When I look behind the PC, the PCI card shows a bright blue LED, which, as for my understanding means everything on that end should be good.
So yeah the only thing i can think of is perhaps to check with a multimeter if the coax cable is faulty?