h115i Platinum User here. Experiencing same problem.
New computer, fresh install. Got everything up and running, installed all my hardware's associated applications and finally began installing some non-essential programs.
As soon as I installed Steam, the problems began. Got USB disconnect notification, connect notification, and reconnect notification. Finally, the USB entry for for the H115 Platinum crashed along with the iCUE service.
At the time, thought my monitor's USB hub was the culprit. May still be some kind of conflict there. Anyway, couldn't resolve the issue and running a 9900k with a pump without some kind of fan control (when it defaults to quiet) is not... ideal. Decided to roll back to a fresh install and go through each step more carefully.
Install #2 proceeded as normal. Until I installed Steam. When the Steam Service started, USB disconnect sound played, lights on fans and pump of the H115i Platinum went berserk. Haven't installed the drivers of my monitor yet, which includes the USB hubs built into them, so I don't know if I'll get the full crashing of the AIO's usb connection or not yet. Saw this thread... apparently I'm not alone.
I have no idea why Steam would be a contributor here, but with 2 separate installations on my PC it there was a direct correlation without any delay. As soon as STEAM's services started, the problems began.