I've also had the issue in the past few weeks, on a 3 month old custom built PC, with the iCUE H150i ELITE LCD XT Liquid CPU Cooler (360mm).
Mobo: Gigabyte Z790 AERO G
GPU: Asus NVIDIA GeForce RTX 4080
I didn't build the PC, it was built for me so I am not really comfortable playing around with the hardware configuration, also the case is Hyte Y60 so really difficult to access things without pulling out components.
What I have tried:
Cold shutdown for 15 mins. This drained the RGB power and worked for a few days but then issue returned
Uninstalling and reinstalling iCue worked for a day, then issue returned (proper, clean install as per instructions)
Forcing firmware update on both the LCD screen and AIO unit - worked once or twice, then issue returned
Now, nothing works, including draining the power completely.
I have raised a ticket, and their advice was to do a clean install even though I already told them I just did that 5 days ago. Fixed for a few days then back to stuck on Liquid Temp. Yesterday I also had the red triangle, but it's back to Liquid Temp today.
Waiting for their next suggestion ...
But I moved away from Asus with this build (I know, except for the GPU) because I was fed up with Armoury Crate and all sorts of issues with the RGB if Armoury broke - and to have this problem after being assured from my local PC store as well as guy who built my PC to go with Corsair as they are 'super reliable' is really disappointing.
Honestly AIO in general has been nothing but a PITA. In my previous build, the Asus ROG Ryujin died (luckily was replaced under warranty with the newer model).