Server system not visible in Defender console after status onboarded

Hello together,

we are currently in a process to onboarding server (diffferent linux and Windows system). In May last year we successfully onboarded around five linux server. Unitl now this devices are running, but not more visible in the defender console. Additional also the devices are not visible in report devices to onboard.

What could be the reason for this?

regards

Carsten