Drobo 5C fan doesn't turn off when in going to sleep

When my Drobo 5C (bought in Mar. 2019) goes to sleep, the fan doesn’t turn off at all.

All drives are off and not spinning, no LEDs are on except the power LED that turns as expected yellow/orange.

Is this common and something Drobo should look into or my unit has an issue?
A big fan continuously running when in sleep is not really a “sleep” function.

(Not that I can put 5C to sleep in any case, as it keeps disconnecting when waking up the Mini (2018) it is attached directly to (with the USB supplied cable from Drobo) running macOS 10.14.4/10.14.5…)