This looks a lot like what i ran into on an older machine after I made some parts fan changes. Almost certainly the parts fan driving the block temp down.
Check it hasn't shifted or changed direction for some reason, and as @Phaedrux said, sock & PID w/ fan on. But also check it mechanically too.
The Duet WiFi build of RRF doesn't support Neopixel, although the Duet 3 build does. Probably the simplest approach is to use an Arduino to drive the Neopixels, and have the Duet send commands to the Arduino over I2C. A complication is that most Arduinos use 5V logic levels, so you would need an I2C level shifter between them.
