Same problem here. I have 10 Riing Quad fans on 2 controllers and I have to reboot my machine multiple times before both controllers are detected. I am completely regret having bought these fans. I had bought fans years ago from Thermaltake and always had problems with the software not running properly. I would have hoped that after that many years they would have solved their software problems, but now not only is the software still terrible and mostly doesn't work (and when it does it chews a ton of CPU usage), but now I can see that the hardware is even more unreliable.
I've spent close to $1,000 dollars on these fans (which look great), but are completely unreliable due to very very poor quality hardware controllers which are only intermittently recognized. If you do a Google search you will see that there are very many of us with this same problem, unfortunately always with Thermaltake fans.
There are some threads on this forum that are 4 years old with similar problems and no responses from tt support. Very disappointing.